The attraction is there instantly. But attraction doesn't last and Sherlock is at a point in his life where he favours stability and the excitement of a new puzzle over the short-lived rush of hormones and sex. That's why he rejects John's attempted flirtation at Angelo's during their first case. The affection grows more slowly. At first it is only fondness and some sort of amazed daze for John's compliments, but how can someone not grow to you when he has shot a serial killer for you?
Admittedly it takes Sherlock a while to recognise that the fondness and the affection have grown into something more, but the easy way they have developed around each other makes it harder to see. They spend so much time in each other's company that the tiny ache he sometimes feels is mostly ignored and definitely not examined closely.
In the end it is a case for which they pretend to be a couple which makes Sherlock see. The casual touches they share to keep up with their cover story are never enough. He finds himself starving for the light trace of John's fingertips on his neck, the brush of a hand against his chest or the easy way their fingers interlace. He soon begins to seek out cases that will allow to use the gay couple routine again, explaining it to John that women are generally more open around gay couples and easier to interrogate.
Sherlock is very proud that their first kiss is not part of such a scenario, that they simply get lost in each other's eyes, in each other's giggles and soon they drink the sound of laughter from the other's lips and exchange it for moans of pleasure. The first sex is of course a rushed affair, with lots of friction and hands and wet mouths, but it is certainly a blissful experience. Sherlock wants more.
He gets more in the sense that from that day on they seldom spend a night separately, that those pretended touches become real ones and the transition seems so easy and floating without any tedious relationship talk or discussions where to sleep. John adapts around him, occasionally putting his foot down when something is important enough to him and Sherlock compromises (sometimes).
It occurs to him that other people must do their relationships wrong because it doesn't seem that complicated as all those advice columns say. He is pretty certain John loves him, although he never says so, but he hasn't said it either (and isn't this considered normal for the British male), so they both know where they stand. And if he feels sometimes a little bit insecure about it, as if it is something that only goes with saying, well that's obviously due to worries about their discrepancies in observation skills or something Mycroft says just to annoy him.
It is one of those cases when the intimacy between them helps to open the witnesses up. Witnesses that are clearly in love with each other, with shared meals and maybe more, but afraid to take the next step and declare their relationship to the world. And it occurs to Sherlock that he wants that, wants to declare to the world that John is his. Not only when he is present, when everybody who has still one functioning sense knows that they are together in every sense of the word. No, he wants the world to know when John is at the surgery or buying milk. And so he abruptly turns to the army doctor at his side to blurt out: "Marry me!"
He expects a hesitant smile, the one when Sherlock does something John considers cute. Or maybe the utterly happy smile another favourite of his. But he certainly doesn't expect John's eyes to darken in sudden anger, his lips to become a thin white line and the shouted 'No' is definitely not on the list of possible reactions.
John turns and marches away. This isn't how it is supposed to be. Right now they should be kissing and Mycroft would text him a date and a location. Well, Mycroft does text him, but his 'That's the most embarrassing thing I've witnessed in recent memory' doesn't help Sherlock in the slightest to understand what had gone wrong.
That twat!
That giant git!
That idiot!
That heartless bastard!
Every step takes John one step away from the scene, away from the latest stunt Sherlock had pulled. Of course, he knows that the detective uses their relationship in his favour, to lure witnesses and suspects in security. Hell, he had even explained why he did it, but John had never thought that Sherlock would go this far, would use a proposal as means to get a breakthrough in a case. Even the lunatic must know that marriage means more to John than a cheap charade, easily dismissed afterwards.
Oh god, when had his life turned into a soap opera, when had this friendship become so much more? When Sherlock had started this (and John was still struggling for the right definition), he had thought this would be enough. At least he would be able to touch. But touching led to caring (well, more caring), caring led to hoping and hoping led to the frantic looking out for clues that Sherlock reciprocated those feelings. Some fleeting moments it seemed as if he was, but Sherlock never said anything, while otherwise being pretty outspoken about everything: The state of Scotland Yard's latest staff additions or his brother's attempts to involve him in another government case. If he felt anything for John, he would have said so, wouldn't he? At least said something before a proposal, for god's sake.
He stops at a park bench, unable to move a step further. The lingering anger is not enough to carry on, he needs time to think. And quite contrary to certain consulting detectives he prefers to do so in silence, prefers his brain to be the only one in agitation while he wonders if (or better how) this will change them, if it would be awkward from now on. Certainly Sherlock had by now deduced how hard his flatmate had fallen for him. Would he care? Would he end this in some sense of kindness to spare John's feelings? Would they continue as before? (As which 'before'? Before the proposal or before the kissing and the sex?)
Several scenarios play through John's head, each more awkward than the other, and each leaving him more and more dreading the next meeting with this infuriating man. He would probably need to look for another flat share, god, he would miss the excitement of the cases. On the bright side, he would be able to keep a job at a surgery without the interruption of Sherlock's cases.
The thought isn't bright enough as is should have been to lighten his mood. In fact, it just cements the awfully dull and grey picture in which John has painted his immediate future and the starting rain just added the right amount of misery to John's considerations. Usually he doesn't allow himself to wade in self-pity, but sitting in the drizzling rain seems like the best of several bad scenarios.
He isn't in the least surprised when a pair of well-known shoes stops right in front of him.
"Why don't you want to marry me, John?"
If anything John has always admired Sherlock's ability to head straight to the core of the problem. But unfortunately that doesn't mean the answer is easy. He wants to marry Sherlock, he just couldn't. Not for the wrong reasons.
It takes Sherlock a few moments to get rid of the witnesses and abandon the case to follow John. He trails behind his army doctor, watching the angry movements and knows from experience that it will make everything even worse if he approaches him now. He follows John to Regent's Park, watches as the other man sinks down on a bench oblivious to his surroundings. He still keeps his distance, his mind whirling with thoughts, all culminating around the questions 'Why had John said 'No'? and 'Why is he so angry?'. The clenching of his fists is always a tell-tale sign for John's emotional condition, far too familiar for Sherlock's liking, although it is not always his fault.
He watches John from under a tree, probably looking ridiculous as if he cares for such things. He ignores the curious glances from the passers-by as he ignores the vibrating of his mobile or the wet drops of rain finding their way through the leaves and on his face. From the involuntary shivers he is pretty sure that tiny streams of rain are running down John's neck and under his jacket and his jumper. And he knows how much John hates this, but still he does nothing to change it.
He isn't aware of the time, just the tiny movements of John and when he notices the agitation is dying away and leaving space for defeat, Sherlock finally approaches him. The detective isn't surprised at John's lack of surprise, they are too well into each other's skin to be surprised at something expected. He is however surprised at the flicker of emotions running over John's face, too fast to decipher them entirely and only giving way to an expression of resolved resolution.
"I said 'No' because marriage is something serious, nothing you just pop out to get a reaction from a witness. Also I'm pretty sure you don't actually want to marry me."
"But I do want to marry you!"
He does not add 'When have I ever said something I didn't mean'. But it is clearly implied and accompanied by a tiny sound of desperation Sherlock can't suppress. And he hopes that John will notice this, while fearing it at the same time.
Sherlock still watches every movement of facial muscles, tiny shifts of emotional display, tries to interpret them, to understand John, but somehow he fails and one of the reasons is his own confusion, his own emotions. That has never happened before.
"Why do you want to marry me?" John finally asks and isn't this the stupidest question he has ever heard.
"Because I love you and you love me", he answers with an air of confidence he doesn't entirely possess, not since the 'No' at least. "Isn't this what people do?"
John sits in front of him, clearly shocked and gaping like a fish which shouldn't look adorable, but it does and Sherlock can't resist the temptation to touch the traces of wonder on John's face. John leans into his touch, a short moment when he closes his eyes and his mouth, before he opens both, but no sound escapes his throat. He tries again and this time in a voice that doesn't sound at all like John and somehow perfectly does, he asks: "You love me?"
It is really a question and that little detail clears the puzzle for the world's only consulting detective: "You didn't know? How could you not know that I love you?"
"You never said anything", defends John himself with only a small amount of indignation. And Sherlock leans down, drawn by the warmth in blue eyes and whispers: "As usually you see, but don't observe."
Whatever John's answer would have been, it is stopped by Sherlock's lips and the immediate surrender of the doctor.
Sherlock takes his time kissing his doctor, kissing away the rain and the cold, lapping the taste of faded anger and wonder before simply drinking the unique taste of John. Their breaths are a little bit ragged when they part and Sherlock has to swallow a lump down his throat, gently wiping wet hair from John's face.
"John Hamish Watson, will you marry me?"
And it takes a breathless second for John to answer: "Yes, I will."
AN: This was written for littlenim on tumblr and Johnlockchallenges Grab Bag Challenge. The prompt was "That's the most embarrassing thing I've witnessed in recent memory." I tried to go for funny, but my muse wouldn't walk with me, instead stayed at the angsty side, so in the end I surrendered.