John Watson isn't sure about Sherlock Holmes right away. He's an odd duck, no denying that, but clearly brilliant. John finds the combination of his intelligence and his refusal to hide it, along with his complete lack of respect for social conventions rather refreshing. Particularly the bit where he treats John like a complete person with some interesting facts about him, instead of as damaged goods.

He's so used to people avoiding looking at him that someone looking so intently at him for long minutes, though unsettling, is like a warm bath.

The flat is lovely and the location perfect, but the flatmate is frankly bonkers and for some reason John likes that. The more people who tell him to stay away from Sherlock Holmes, the more stubbornly he sticks to him. He is aware, vaguely, that the man is showing off for him, trying to please him in an odd way, and that this is unusual. Not the showing off, the wanting approval from someone who, really, shouldn't matter to him one bit.

Despite not being at all sure about Sherlock Holmes, John Watson follows him to a crime scene. And keeps following him, at a walk, at a run, into danger, so quickly that he soon finds he's left his old life and his limp somewhere out there in the dark streets of London.

He knew the pain there hadn't been real. How could it take a near-stranger to prove it to him?

When Sherlock Holmes first casually refers to them as "we", not 36 hours into their acquaintance, John Watson feels a strange swell of pleasure and pride. Pleasure at being part of a team again, part of anything, when he's been alone for so long, and pride that this brilliant man seems to find his opinion and aid worth seeking out. And suddenly John can't imagine a life that doesn't include him.

It's not very long before John realises something more than a solid friendship is developing here. He takes it in stride. He's never been one to lie to himself, and he doesn't see the point of doing so now. Men have never featured in his romantic activities (except, occasionally, in the way that tends to happen during a long and isolated deployment), but he is not entirely opposed to the concept and Sherlock is certainly very unique.

He's never been inclined to worshipful obsession or infatuation, but if he were, this would be the time.

As his attraction and attachment to the man continues to grow, he is not unaware of his friend's hungry stares, abruptly terminated if John turns toward him. Sherlock stands closer to him and doesn't realise. Sherlock grow more intolerant of long absences on John's part. Sherlock takes obvious delight in any move John makes to protect or defend him. John notices all of this, but he's not sure Sherlock does.

John wonders which of them will break first. He hopes it's Sherlock, not because he wishes to delay the inevitable, but because he's not sure that Sherlock could accept it until he fully comes to terms with his own poorly delineated feelings. So John stays quiet, ignoring the blatant signs as thoroughly as Sherlock manages to do, waiting for him to figure things out.

Maybe Sherlock never will. Maybe he's not capable or interested, as he claims. Maybe it's all in John's head.

After the horrible incident in the abattoir, in which Sherlock comes closer than he knows to dying and John kills a man with more raw brutality than he has ever before displayed, things have no hope of staying the same. As Sherlock whispers to him deliriously about beauty and starlight and the suns that live in John's chest, and John cannot stop himself from kissing the top of Sherlock's head as he holds him to try and warm his hypothermic body, John knows they will not be able to resist each other much longer. It both delights and terrifies him.

He could have lost him. It was a close thing. John would claw through more than old bricks and mortar to stop that from happening.

When Sherlock comes home from hospital his stares grow predatory and intense, and he is worse at hiding them. John can feel desire radiating off him like a physical force whenever they are even remotely near each other. It takes all his restraint not to jump him the first time it happens, but he wants Sherlock to come to the conclusion on his own.

He makes it very nearly four weeks. Very nearly four weeks of cold showers, turning in early to avoid late night temptation, and studiously keeping at least one piece of furniture between them at all times. And then one afternoon, when Sherlock is sprawled gracefully on the sofa, deep inside his own head and miles away, unaware of how the sunlight is making his hair shine and his skin look even more like ivory than usual, John breaks.

He's never before felt like he can't physically keep himself from another person any longer. But that's what he feels now and it beats his rationality into submission.

He is surprised at how much coaxing it takes for a man so obviously smitten, and begins to second-guess himself, wondering if he has misinterpreted all the signs. But once they meet in that first kiss, so soft and wet, Sherlock's body trembling beneath his, wanting to respond even while being completely overwhelmed, John knows there is no turning back. That would be like death, he suspects, for both of them.

When he is laid out on top of his friend, listening to his heartbeat and stroking his hair, John is overcome with amazement that he is allowed to do even these simple things – touch, kiss, hold – to a man who has always seemed so untouchable in every way. Sherlock says he wants everything, and John knows he's not just talking of the things they can do with and to each other. He wants every last thing John has and is, and he's not promising he'll give anything back.

And John will do it, because with this man it's all or nothing and he can't bear to go back to nothing.

When the time finally comes, much later that night after both men have acclimated themselves to the sudden lack of boundaries and the reciprocal desire of the other, John feels like he has live current running through him. He had expected Sherlock to be wild, rough even, aggressive from long-restrained desire; he is prepared for that. What John does not expect is the hesitant but determined Sherlock, a little unsure of himself, still somewhat convinced this is all an illusion and one false move will make it vanish.

John is certain that this will not be the usual way of things between them, but is grateful for it this time. He himself is a little unsure, although he is positive it is completely real. He feels like he is being shocked every time Sherlock touches him in a new place, removes an item of clothing, mouths unknown words silently into his neck or shoulder. Like he is on the verge of dying and being yanked back to life each time. His skin feels hot everywhere Sherlock's hands go, though the taller man himself is cool, as if he is drawing all of John's warmth to the surface and into himself.

Even through all his fantasising over the past months, John hadn't actually believed those large hands with their long, sensitive fingers would ever really be roaming over his body like it was a thing to be studied as carefully as the types of tobacco ash.

John takes an elemental pleasure in finally being able to do some of the things he's tried not to obsess over, simple things like fisting both hands in Sherlock's impossibly thick hair as Sherlock attempts to taste John's trachea. Like burying his face in that elegant line where Sherlock's torso meets his thigh and licking, lower and lower, until Sherlock gasps despite himself, John's lips wrapped around him and his face buried in a completely different landscape, tangled and dark and glossy.

Sherlock in turn puts his mouth to the ugly, intricate scar that mars both the front and back of John's left shoulder and sets himself to tracing each and every white line of it, starting at the outside and working clockwise towards the centre. It's as is if he wants to lick the poison out of it, or maybe just learn it by heart. John understands that this is the most tender thing Sherlock can think to do to him, and lets himself be taken by the soft and pleasing sensation of Sherlock's tongue wandering over his bare skin.

He knows Sherlock both loves this mark of destruction on him and also wants to undo all the damage, and John believes he might actually be capable of it.

When Sherlock is at last nestled deep inside of John, where no one else has ever been or ever will be, he looks down into John's eyes with an expression of joyful disbelief, perfectly still, perfectly at ease.

John cannot believe how complete he feels, or the level to which he aches for more. He wants to be taken, to be filled, in a way that is completely unfamiliar, but suddenly as necessary as breathing.

"I think you might be radioactive," Sherlock tells him, completely serious, and John quivers as the reverberations of Sherlock's deep voice reach into his own body.

"Like a bomb?" John manages, trying to distract himself, as even staying motionless together is nearly enough to finish him off now. .

"No… like a pulsar or a white dwarf. Compact but bright and powerful."

That is the closest thing to romance John is likely to get, and he treasures the strangeness of it. And then Sherlock begins to move and all thoughts are seared from John's head. It's over far too soon and yet they seem to exist timelessly in those few moments.

Nothing has ever hit him like this. Nothing else will ever be enough again.

When they are finished, shuddering sharply only seconds apart despite Sherlock not laying a finger on John to bring him off, Sherlock rolls John on top of him and they lay there, chests together, breathing in sync. Sherlock seems to like having John on him like this, likes to feel the weight and heat and solidness of him to assure himself it's real.

"So, if I'm a white dwarf star, what does that make you?" John asks, when the afterglow has dimmed enough to speak.

"Hmm. A black hole, perhaps."

"A dead, collapsed star that sucks in and destroys everything around it?"

"Maybe."

John put his lips briefly to Sherlock's collarbone. "I don't like that."

"It's true."

It might be true, but John won't stand for it. Sherlock deserves better, even if he does take and destroy and is generally a force impossible to resist.

John shakes his head. "If you must be a dark thing, be a dark nebula. They're full of energy and they draw light to themselves but they don't destroy. They do really shine, but beyond the spectrum of the human eye."

He can feel Sherlock raise an eyebrow.

"I had a telescope in the fifth form. I like astronomy."

"A dark nebula," Sherlock says, pondering. "If you prefer." He pauses for a long minute. "Did you mean it?"

"Mean what?"

"Everything. That I could have everything."

John grins to himself. "I would think that should be obvious by now, but yes. Tattoo your name on my heart, I'm all yours." Sherlock perks up noticeably and John amends, "Not literally. We will not be tattooing internal organs. Or anything else."

Oh Lord, he would do it, he really would. John isn't sure if he's appalled or flattered.

"It's possible though," Sherlock presses.

"And sometimes fatal. No. But that doesn't make me any less yours."

Sherlock seems temporarily satisfied by this and goes nearly limp, settling into the pillows. John goes to move off him, but is restrained by an immoveable arm, and decides that of all the places he could possibly sleep, on top of Sherlock Holmes is one of the better ones. And so ends the first day of what must be called a relationship, if only for lack of a more sufficient word for it.

Sherlock Holmes is a fucking nightmare. And John Watson loves every minute of it. He had known that this was how it would be; any kind of relationship with Sherlock had to be, on some level, hellish. But knowing it and living it are very different things. Not that he has regrets, it's just a lot to deal with. But he loves it, all of it. Well, almost all of it.

He loves the late night chases, the danger, the spark of energy that come with them. He loves the difficult cases, watching Sherlock's clever mind at work, wheels turning almost visibly. He loves the long hours in bed (or not) together, and all of Sherlock's insane, inventive, and strangely erotic ideas for what to do with them. He even loves Sherlock's weird possessiveness, his wild mood swings, his inappropriate comments. He could go on and on about the things he loves about Sherlock Holmes.

But he won't because he's an Englishman and a soldier and it doesn't work that way. It's enough to know them for himself.

There are some things John Watson doesn't love. He hates the way Sherlock can, in less than a minute, go from sweetly affectionate to using everything he's learned about John, even the most intimate knowledge, to eviscerate him verbally. He hates the way Sherlock expects, demands, instant forgiveness for even the most cutting cruelty, or sometimes doesn't even realise he needs any at all. And he really hates the way Sherlock can disappear for hours or days without notice, making him ache with worry that his friend has discovered a new and interesting way to get himself killed.

And yet even those things John still truly loves somehow, no matter how painful or terrifying they are, because they are part of what makes Sherlock the man he is, the man John would never dare to wish to change.

As for the man himself… John knows he is not permitted to say the words to him. Sherlock, so disdainful of all sentiment, would view it as evidence of the weakness of John's devotion to him, not its strength. So he tells him he's mad and cracked and disturbed and a danger to society. He calls him a git and an idiot and a prat and a twat and every other name he can think of and Sherlock beams like John has written him a sonnet or carved his name into his chest.

For Sherlock's part, whenever he growls "mine" to John at random and decreasing intervals, bites him in a place nearly impossible to cover when he goes out, snaps in annoyance "hurry up, I need you", or pulls John to him suddenly, roughly, twanging with desire, John finds that he could not possibly feel more cherished by anyone. He wonders if something is wrong with him, then decides he doesn't want to know because it wouldn't change a thing.

It's not something that could ever be considered a healthy relationship, he knows, but in all his healthy, balanced relationships he never felt like this. And what other kind of relationship can you have with a madman?