Disclaimer: I do not own Sherlock.

Sherlock had decided early on that there was something almost sacred about having a flatmate.

Sherlock, naturally, didn't hold many things sacred, but every now and then there was something that made the cut— his mind, logic, science, the perfect cup of tea— and, lately, Sherlock's fascination had revolved around the state of being a flatmate, and of having one.

There really was something about having to live with another person, cooperating to some degree, which interested him. For instance, he had noted that he was far kinder to John than he was to nearly anyone else, with the possible but not certain exception of his mother.

Also, he knew absolutely everything about there was to know about John Hamish Watson.

He was used to knowing everything about a person by looking at them (which was hardly a secret) but somehow this was different. Not only did Sherlock know the important things about John, like his job (doctor) or if he was cheating on someone (he wasn't) or whether he was right- or left-handed (left), but he knew all the worthless little details that he would have deleted were they about anyone else. Little things, down to how thoroughly John chewed his food before swallowing. Minutiae, useless.

Sherlock was even certain he could have worked it all out without being extraordinary at all, and simply because they were flatmates. As someone who had always avoided human contact like the plague itself, he was staggered by the sheer volume of time they were forced to interact with one another. The sense of safety one felt at home meant that guards went down the moment one walked through the door. Even John, the traumatized army doctor, the moment he removed his jacket and hung it up. Even Sherlock himself, once the scarf came off his neck.

As such, John knew nearly everything about him, as well, and Sherlock couldn't help the little thrill that gave him— and he'd tried to. John knew his chaotic sleep schedule (which was more like a set of circumstances under which he would sleep than an actual schedule), knew what foods Sherlock liked and how to force him to eat them, knew what he thought made a chair superior to other chairs. John knew that on Thursdays Sherlock would not play his violin for any reason and that he liked mint tea when it rained because it reminded him of the more pleasant moments of his childhood.

Sherlock wasn't used to being known like that by anyone in the world but his brother. He (well, Mycroft) had paid extra for Sherlock to have his own dorm room in Uni for fear that he'd murder (or be murdered by) anyone he tried to cohabitate with, so this 'flatmate' thing was new. He'd made a few attempts before John but they hardly counted, running away after only a few days like they did. So, Sherlock amended, perhaps it was having the right flatmate that was sacred.

For the first time, Sherlock was experiencing implicit trust. He had been surprised to notice, quite suddenly, that he trusted John— not just to refrain from killing him in his sleep, but to not go around disclosing all of Sherlock's personal habits, especially the embarrassing ones and the ones that did injustice to his intellect. Similarly, he had noticed himself doing the same for John, even when it was inconvenient for him, like going out of his way to avoid revealing John's nightmares or secret fondness for kittens.

Sherlock was self-aware enough to know that doing something that was inopportune for him for the sake of another person's privacy was a serious reflection on his feelings about the person.

Then, of course, there were all the little domestic things, and these were things that Sherlock had never even gotten from Mycroft. He got a strange, warm feeling, for example, when splitting the costs of things between them, usually groceries. They both ate them (although John ate far more), so it was only right that they both paid for them. He also liked paying for John's half of the rent when John couldn't. Sherlock liked eating together, enjoyed making note of what Chinese John ordered most and occasionally bringing it home without warning in order to surprise and please him. He liked watching television with him in their downtime, trying to negotiate what to watch and resorting to any means necessary to get the channel of his choice. Even more, he liked the programs they didn't have to argue/cajole/threaten the other about: cop shows. Sherlock liked deducing the sorry excuses for mysteries and John liked hearing him do it (brilliant! fantastic! wonderful!).

He would never admit it out loud, but Sherlock even loved the things most people would call awkward, simply because they were so... trusting? Domestic? Companionate? Yes, companionate. The inevitability of accidentally seeing each other naked, for example. Worse, walking in on each other (more precisely, Sherlock walking in on John with some woman) but having the decency to whip around and walk back out without a word and without bringing it up later. (If John ever asked why Sherlock never brought it up, never questioned him about it like he was apt to do about everything else, Sherlock would have said, "Because we're flatmates" and John wouldn't have understood, Sherlock knew. Of course he wouldn't— John had actually felt 'companionship' before, so for him this was nothing novel.)

Sherlock had learned how to navigate around another person, both physically to avoid collision and in terms of scheduling, including bathroom. Not that Sherlock was overly accommodating (John would protest the suggestion that Sherlock wasaccommodating at all, actually), but to some degree he had to make room for John's life. A very, very small degree. While he could expect John to come running back from Bart's at his command, he figured he did need to at least know that John was at the hospital, and that meant knowing another person's schedule.

John did plenty of things that annoyed him, but everyone did things that annoyed Sherlock so he wasn't impressed by this. On the contrary, the things Sherlock delighted in noticing were the idiosyncrasies that should have annoyed him, but didn't, because they were flatmates. Like John's horrid sense (lack) of style. The fact that he could literally be happy making tea at any time of the day, 24/7, and the accompanying screaming kettle at 3 AM. The loud, angry phone calls to Harry. His habit of leaving shoes all over the place. His absolute refusal, under any circumstances, come hell or high water, to eat breakfast without something smeared in marmalade. And, far less funny, all the shouting he still did in his sleep. Because he may miss the war, Mycroft was right about that, but it had certainly involved a lot of blood and he was still a doctor who didn't like being unable to save people.

Sherlock had deigned to sleep, and was curled up in his bed, almost smiling at the muffled sounds of John making tea in the middle of the night, trying to keep it down but failing, as always. He thought about getting up and offering John some late-night company, because they were flatmates, but because they were flatmates he also knew that John preferred his late-night tea alone and that the doctor in him would be annoyed if Sherlock sacrificed rare sleep for something as petty as company-keeping ("Sherlock, I've had tea in Afghanistan, ducking bombs as they dropped from the sky, surrounded by enemies with guns. I think I can manage in our flat").

Instead, Sherlock simply rolled over and closed his eyes, trying to remember if that was the procedure for this 'going to bed' nonsense that he so devoutly avoided, usually. He listened to the sounds of John pouring out his tea, taking it over to his chair and sitting down, and to his curses as he burned himself, which he always did.

Sherlock knew that John would be up and about for approximately twenty minutes, enjoying his tea. He would work on his blog, surf the internet, or read a novel. After that, he would stand up, stretch, and head back to bed.

He liked knowing this about John. He liked that John probably (definitely) knew similar things about him. And the very best part of it was that, for the first time in his life, no one would think Sherlock a stalker for knowing all these things about a person.

It was expected. It was... normal.

Sherlock was not used to feeling normal, and as uncomfortable as the idea made him, it was kind of a nice change.

Sort of like how it was a nice change to have a friend.

Especially one as good as John, even with his jumpers and his strewn shoes and his marmalade.