McCoy spends the first six weeks on board of the Enterprise muttering to Jim about unfeeling hobgoblins and the undeniable stupidity of having a green-blooded supercomputer as the executive officer, and the first day of the seventh leaning back against the bulkhead in someone's (Spock's?) quarters, the lips of the Vulcan in question stretched around his cock.

He couldn't tell how they ended up here, though Chekov's alcohol-filled birthday party, Spock and Uhura deciding they're just good friends after all, and a debate for the ages (McCoy will never agree that the results of low-speed dermal regeneration are not significantly different from rapid, no matter what those assholes at the Andorian Science Institute publish, so take you evidence based practice and shove it where Eridani doesn't shine) might have had something to do with it.

He's drunk, and it's been, oh lord, since long before the Narada, and he would gladly stab Spock with his rustiest scalpel on his best day. But when his mouth is full with McCoy's come and he finally cannot say shit like 'highly illogical', or 'most inefficient', he can't help but admire the dusting of green on slanted cheekbones, its contrast with the dark, hugely dilated pupils currently looking up at him, and the well-muscled, tapered back blocking McCoy's view of his own damn feet.

Which must be why after he's poured months of self-restraint down the Vulcan's tight throat he doesn't just zip his pants and stumble into the hallway to go get his head checked by the ship shrink. Instead, he hauls Spock up, turns them so that Spock's the one pressed against the wall, and takes his hard-rock, leaking, preternaturally hot dick in his hand and gets him off while they French kiss as if they were sixteen and behind the bleachers.

Then he does stumble into his own cabin, where Spock's moans echo inside his skull until the break of the artificial dawn.

...

The morning after, he hypos himself awake while wondering if he should lay off the bourbon for a while, because that was a weird-ass sex dream he just had.

Spock is a jerk. McCoy is still on the fence about whether he can be counted on to have Jim's back, and endangered or not, he will not hesitate to throttle him the next time he accuses his Med Bay of being chaotic. He can keep out of his alcohol-fueled wet dreams, thank you very much.

And then, he finds his impeccably folded, meticulously ironed, recently laundered blue uniform jersey neatly laid out on his office desk. Whoever did it must have used a freaking ruler.

He feels a first stirring of dread in the pit of his stomach.

The second comes two hours later, when he arrives on the bridge right the minute Spock is waiting outside the turbolift, hands clasped behind his back. In an unprecedented twist the Vulcan doesn't meet his eyes, nor he acknowledges McCoy in any way.

Suspicious, Bones turns to follow Spock's movements as he boards the lift, and notices a medium-sized, sallow bruise at the base of his neck, peeking out of the uniform undershirt.

He closes his eyes.

Fuck my life, he thinks, and then he says it out loud, for good measure.

...

He was drunk. Roofied, perhaps? That's the only possible explanation.

He was drunk, and horny, and had no clue what, or whom, he was doing.

That's his excuse, and he's sticking to it.

Not sure what Spock's is, but that's none of McCoy's business.

...

Getting married to a serial cheater who considered pre-breakfast rip-roaring insult matches as the ultimate form of entertainment while he was still attending med school gifted McCoy with great compartmentalizing skills. So he just doesn't think about it, not for months, except maybe during the odd, lonely shower.

He realizes that he and Spock haven't exchanged more than thirty words since it happened when they are directly across from each other on the shuttle heading to Herliq 6, buckled to their seats in a way that leaves little chance of not catching each other's eyes every few seconds.

He realizes it even harder when they are separated from the rest of the party because they are being chased by some animal that is glowing so brilliantly that it must be radioactive.

"The fuck was that?"

They're crouching behind something that looks suspiciously like moss, if moss smelled like five-day-old fish.

"Unclear."

McCoy snorts. "That's helpful, mister science officer."

Spock gives him a look full of disdain. "I could wildly and baselessly speculate, of course, but that is your specialty, Doctor."

"Right, because yours is reading the sensors, and clearly you did that so well. Commander."

They stare at each other combatively, McCoy's mouth as thin as Spock's eyes are narrow. McCoy braces himself for a cutting retort, but Spock abruptly drops his gaze to the purplish ground, an olive sheen coloring the tip of his ears.

The fuck is this, McCoy wonders, silently this time.

He clears is throat and is reaching for something belligerent to add when Hendorff, god bless him, finds them with reinforcements.

During the ride back to the Enterprise, and in the hours they spend side by side in the decontamination chamber, there is no further bickering.

...

The following day brings a murderous rage, and McCoy has to order himself to calm down a dozen times.

He's counting to one hundred when he blindly grabs a handful of hypos from the tray he methodically laid down as soon as he got to Med Bay; when the security ensigns on the turbolift sense his seething rage and give him a wide berth; when he stomps in the hallway outside of Spock's quarters.

He reaches eighty-nine while he uses his medical override to open the door of Spock's cabin, only to find the Vulcan meditating cross-legged on the floor, wearing Starfleet issued sweatpants and a t-shirt that reads 'Come to the math side, we've got pi.' It's got to be a present from Uhura.

The casual, Terran domesticity of his attire clashes magnificently with the pointed ears, diagonal eyebrows and still excessively green pallor.

McCoy shakes off his unwanted fascination.

"You needed this injected thirty minutes ago, commander moron. But no, I bet getting actual treatment for radiation poisoning is illogical, uh? Surak wrote down on his sheepskin scroll that real Vulcans should just meditate contaminating agents out of their system, didn't he?"

Spock blinks hazily. "Doctor, I was about to—"

McCoy drags over two hundred pounds of Vulcan up by the ear and hypos him as painfully as possible, rejoicing when he sees him actually flinch. He's about to give him a second (unnecessary) shot, just for kicks, but Spock puts his hand around McCoy's and stares him down, and then, somehow, Spock' lower back is warm underneath his palm and McCoy is turning him and pushing him down on the still unmade bed, and it's not five minutes before he's sliding inside him like a hot knife through butter.

The pleasure is crippling.

For Spock too, apparently, because he says "More," several times, in a voice that McCoy didn't think he would ever be able to produce, and he can only answer in kind, groaning in his ear to "Be quiet," and "Be still," and "Be good, and I'll give it to you."

Their hands clasp together at Spock's waist, and McCoy gasps his orgasm against his nape, coming like a dam breaking.

It's sublime. And how pathetic does it make him, that he just fucked a guy he's in a mutually hating relationship with?

He wants it again.

Afterwards, he staggers out of Spock's quarters without saying a word, and when he sees Jim in the turbolift he stabs him violently with a vitamin hypo he picked up by mistake.

...

That very day, Spock sits next to him at lunch.

He does it with a bit of a flush on his cheeks and keeping his eyes mostly on his salad. If he's appalled by McCoy's dietary choices (fried chicken), he manages to keep his disapproval to himself.

Luckily, McCoy muses, they don't need to make conversation, because Chekov and Sulu are sitting with them and there's no shutting them up. Which doesn't explain how they get into an argument over the new Federation guidelines on translational biomedical research, which are too damn strict if you ever want to have any significant type of advancement that has the potential to really benefit patien—

McCoy is baffled, and irritated, and doesn't even finish his rice before heading back to Med Bay.

The following night the Vulcan shows up for the first time to the monthly history club meeting, during which McCoy screens an old Terran holomentary about the American Civil War. He is full of relevant questions, and "I see," and "Fascinating."

McCoy is going to murder him, and he's gonna make it slow.

Two days later, when their gym visits overlap, Spock asks McCoy to spar with him in a weird, stammering voice.

McCoy doesn't even answer and storms out, sure that he's being played even though he can't figure out why.

...

There is an outbreak of the Cardassian flu because no one fucking takes McCoy's painstakingly produced prevention guidelines seriously if they even read them at all, and yes, the flu cycles through quickly, but that doesn't count if it's cycling through the whole freaking crew, and for the twenty-four hours it's symptomatic it can be pretty devastating. He told them so, dammit.

He's been holed up in Med Bay for at least seventy-two hours and he's on a very non-restorative paperwork break in his office when Spock shows up at his door, bearing a tray and staring at his own uniform boots, skin greener than usual.

The tray carries grilled chicken with a side of potatoes and green beans. McCoy's mouth waters, and after three hours of sleep in the same number of days he's not quite sure at what biologically relevant stimulus, precisely.

He eats grudgingly, but the food tastes amazing and Spock sits in front of him and cracks a few snarky remarks about how complicated it must be for the crew to correctly follow hygiene protocols and the multiple engineering degrees doubtlessly required to operate the sonics and wash one's hands, and McCoy can't help but snicker around a mouthful of potatoes.

When he's done, they just stare at each other in silence for a few seconds, a flicker of tension blooming in McCoy's chest, and then Spock stands up and manually locks the door.

This time they have lube, because guess what, McCoy's a doctor and he keeps a little bit of everything in his office, so they don't have to make do with what the Vulcan body naturally produces.

He bends Spock over and fingers him open like he's been thinking about increasingly often, first one finger, then two, then three, and then curling his whole fist inside the hot, greedy, welcoming body. Spock sighs and throws his head back like this is all he came here, to Med Bay, to the Enterprise, to Starfleet, to fucking space for. His eyes are deliciously glassy, and McCoy can't stop staring at him while Spock ejaculates all over the couch.

He brings himself off between Spock's rounded cheeks, exhaling out the misery and fatigue of the past few days.

He wonders what it says of him that the best part of his week was watching Spock come apart.

...

It becomes a habit.

A bad one, like drinking bourbon before bed, or putting in even more hours at the clinic when he had a feeling that Jocelyn was fooling around on him.

One that he cannot break easily.

He finds himself slipping inside Spock in the deserted Med Bay at the tail end of gamma shift, or taking his fingers inside his mouth until the Vulcan falls apart right off the hangar bay.

For shore leave on Starbase 8, he books a hotel room where he ends up staying a grand total of five minutes, because the rest is spent in Spock's bed, sucking green marks into his skin and pounding him into the mattress until neither of them can get it up anymore.

One night Spock shows up in his cabin for something genuinely work related, and they end up sixty-nining and sticky with each other's sweat and come.

Spock is not, McCoy has to admit reluctantly, as bad as he initially thought.

Yes, he's a prick with a stick up his ass, but not as insufferable as he originally seemed. Most of the comments he makes are insulting to the human specie in general and to McCoy as the prototype of the illogical human in particular, but they come from a specific cultural context and mostly from a good place. He can be counted on to always voice the fairest solution to every problem, no matter how unpopular it might be, and he treats those around him with unfailing kindness and patience.

If he's a little fixated on the whole logic thing, well… maybe he can't be blamed too harshly, since the whole business of his planet being blown up can probably justify a little reactionary attachment to traditions and such.

And it's obvious that he does feel. McCoy doesn't know how he missed it before, but all the emotions are there, only occasionally betrayed by an almost imperceptible sigh, the upturned corner of a mouth, a hand clutching the sheets.

McCoy compartmentalizes, and doesn't think about it.

...

Except for the occasional mission together, and general department head briefings, on a ship of eight hundred souls they wouldn't cross each other socially more than once in a blue moon.

But that doesn't account for the fact that Spock is giving McCoy a run for his money when it comes to being Jim's best friend—not that he's jealous, he loves the kid like the little brother he never asked for but Jim did kind of leech onto him to begin with and he definitely needs a more active social life than McCoy cares to provide him with.

Having Jim in common with Spock is handy, because it's nice to share parental custody when dealing with a handful of potential catastrophe in a pretty blue-eyed package.

But it also sucks, because they are thrown together all the freaking time when they have to go along with their Captain to prevent his antics from causing interplanetary conflicts or the contraction of lethal STDs, and after a good day's work he and Spock usually walk to McCoy's quarters, where he proceeds to fuck the Vulcan's brains out.

Thing is, the two things seem almost… seamless sometimes, like going on a Jim-babysitting date, and then returning home to unwind, and no. This is not what is going here.

It's a goddamn slippery slope, and McCoy's sliding down like he's got oil under his butt, which makes him try all the fiercer to climb back up with his nails.

Still, people notice.

That McCoy's left eye doesn't twitch with fury as much when Spock declares that something is 'typically human'. That Spock has been dutifully reporting to Med Bay for his post-mission check ups. And that even if the levels of sass between them are still sky-high, neither seems to be going quite for the jugular, these days.

First Uhura, and then Sulu, and then finally Jim, they use words like 'chummy', and 'shared hobbies', and one day, after he and Spock work together on a particularly grueling mission, McCoy thinks he overhears them saying something about 'harmony'.

McCoy intensely hates all of them, and silently upps the frequency of their physicals.

...

And then comes the 'routine mission'.

Which is for all intents and purposes really a routine mission, except for the twist towards the end.

Twenty-three people beam down, eleven beam up, and seven walk out of Med Bay.

McCoy doesn't need to join Spock on the math side to know that it's less than a thirty-three percent survival rate.

Two weeks after the mission, when the last of the fortunate seven is finally discharged after extensive care, he heads blindly to Spock's cabin, only to find that Jim is in there, playing one of their games of chess, looking up at McCoy with surprise.

"Bones! Were you looking for me? I think I left my comm in my…"

Jim's voice trails off as he looks back and forth between his friends, who are currently ignoring him, and to the almost tangible tension that materialized as soon as their eyes met.

Spock reacts first. "Jim, could you leave us, please?"

He doesn't take his eyes away from McCoy, and McCoy doesn't spare a glance for Jim's widening stare or for his retreat through the shared bathroom. He just knows that when he and Spock are alone he finally feels his heart beating for the first time since that useless, blood-filled shitshow.

Spock walks up to him and wraps his hand around McCoy's wrist, leading him to his bed and lightly pushing on his shoulders until McCoy's sitting down. He takes off McCoy's boots, and then his own, and then they are lying down, arms wrapped around each other and McCoy can finally just hide his face in Spock's neck, smell him, and start remembering how to breathe.

"Leonard," Spock sighs.

Yes, he thinks nonsensically. Yes.

...

It's all about faulty connections, he muses.

The issue has to be that his heart not very well connected with his brain, because he's positive that if he was able to pass xenoimmunology with high honors he must know better than to fall so deep for a Vulcan, even as he keeps tumbling down with no sign of deceleration in sight.

It's just this goddamn slope, which gets more steep and slippery by the goddamn hour.

He's helpless to stop the gradual but steady desertification of the atmosphere in his quarters, or the tins of tea leaves piling up in his liquor cabinet.

He tells himself that it's a small price to pay for the best sex of his life, but then a crisis arises and they find themselves physically too exhausted to knock boots for long stretches, and there is no question of Spock not sleeping in McCoy's cabin because of it.

When they pick up some three hundred refugees from Altair 5 to shuttle them to Andor, the Enterprise is packed like a sardine can and the crew needs to double up quarters. Jim, who has long stopped winking and giggling at the idea of Spock and McCoy together, orders Spock to pack up, move into Bones' cabin, and hand his over to two of the refugees without batting an eye.

When they depart from Andor Spock doesn't move out.

McCoy's descent picks up some more speed.

...

They plan shore leave together.

They visit Georgia, where Spock delights McCoy's mother by pretending not to understand idioms like it's an Olympic sport.

The corner of Spock's mouth lifts when McCoy says things like, "When I was young this all used to be countryside," and his gaze is indulgent when he comments that, "Given the circumstances, it is fortunate that your lifespan exceeds a Vulcan's, Leonard," before kissing him softly on the cheek.

...

When Starfleet changes those stupid, useless, unrealistic, impractical, goddamn illogical rules about fraternization, they just have to get married.

It's only a form, a signature, that doesn't mean anything except that he and Spock can continue as they are on the Enterprise, and push Jim's suicidal ass out of phaser fire or prescribe him suppositories against pollen allergies.

McCoy already went through a wretched bride-centered beauty pageant excuse for a wedding once before, anyway, with the stupid bird-killing rice and the excruciatingly awkward first dance, so this should be no more than brushing a spec of dust off his shoulder by comparison.

And yet, it feels momentous.

It feels colossal, and engulfing, and warm, and for a moment McCoy's fingers, that remained firm two weeks ago while his best friend's blessed heart briefly stopped right in his hands, tremble and clench around the stylo for a minute. It's huge. It's a cliff, and it's a tsunami.

Spock knows, like Spock always does. With clear, open eyes he covers McCoy's hand with his warmer one and slips the stylo out of his grip, signing first, his handwriting neat and readable.

It feels like an honor, and like the most natural thing in the universe, to add his sprawling, slanted name next to it.

McCoy hits the ground with a thump.