It is so tiresome, having to explain things to John when all he really wants to do is watch the light fall on John's face or listen to John scold him in that delightfully proprietary way he has, as if John is the one who will be inconvenienced if Sherlock falls down in a dead faint from malnutrition the way that John keeps threatening in his most impressive trust me I'm a doctor voice. John has many tricks up his sleeve and the bothersome thing is that they all seem to work on Sherlock.
It is wretched, but once Sherlock starts to answer John's idiotic inquiry about why he needs to move out of the flat, words start pouring out of his mouth like water crashing through a weak dam, and before he can catch hold of its iridescent tail, the fish that proclaims his love for John has darted free, propelled forward by the force of Sherlock's stupid, stupid longing.
He'd gone back and totted up figures – and been angered all over again by his own former idiocy when dredging his memory for clues about his cocaine years yielded nothing – and fully seventy-three percent of his cases had some toxic love story as a catalyst, with another eighteen percent bearing a more than tangential relation to homicide. Murder was just one way love blossomed, choking the air with its rank perfume. Sherlock wanted desperately to keep the air between them, the air of their shared flat, clean. There should be no trace of poison in the air once John left, when all he had were his memories of the man who rejoiced in his brainwork.
He could not fathom looking at John and deciding that his eyes would be more beautiful without their light, that his vocal cords would be more pleasing if severed, that the quick rise and fall of his chest should be stilled. John was John, and he needed to continue to be just as he was until he simply couldn't anymore, and above all Sherlock wanted to play no part in that moment of reckoning. All he could do was delay it as best he could, by safeguarding John and sending him on his way after John forced the issue with that one soft kiss; Sherlock had felt dizzy and sick with longing for pressure from John's strong arms instead of the wall. And something had gone cold in his belly just then, with John's careful lips working against his, because he had foreseen this conversation and how long it would take John to draw the obvious conclusion.
He's still taut, tense, unhappy when John's voice animates some useless bromide about love being a two-way street. What would be the point of that, he travelling in one direction and John in the other, perhaps meeting only briefly at some indeterminate place, perhaps meeting others before and after? He closes his eyes briefly at John's stupidity, at his own weakness for John's easy acceptance of these pointless homilies. It does not even serve a purpose; he has no greater insight into murderers' minds for loving John. All he has that he didn't have before are knots of frustration choking his muscles, itches running along his skin like a disease.
John is not even listening, too busy spinning out fairy tales as if he were newly hatched and not the steady and practical man whom Sherlock loves against his will. What is he saying? They cannot grow old together for the simple reason that Sherlock does not plan to grow old at all. He will inevitably die in pursuit of his profession – die with his boots on, as a soldier like John should appreciate – and will therefore be spared the indignities of age and infirmity. Though John has a will just as strong, and if anyone could keep Sherlock alive by dint of judicious nagging and sheer cussedness, it would be John; under John's dictatorship in the kitchen, Sherlock has put on six pounds, and thanks to John's morality, Sherlock has stayed clean.
". . . love you back," Sherlock hears, and the cold fist in his belly bursts open, a shot of warmth hitting his senses. John has a peculiar look on his face now, one that Sherlock is quite sure John never had to make before meeting him; it pleases him to think that he has altered John as surely as John has altered him. "I've killed someone for you already," John says, and Sherlock takes his time, looking at John's steady trigger finger, at the quiet pulse at his throat, at his eyes dark with sincerity.
"Yes," he agrees; John has killed for him. More precisely, John has saved his life and is declaring his interest in continuing to shape Sherlock's future. Sherlock feels his skin start to sing at the thought of the puzzles that John will watch him solve, the moments when John will speak the one word Sherlock needs to crack the case. "Stay," he demands, and John's kiss is very nearly answer enough. "Stay," he says again, and John nods, the movement doing nothing to hide his smile.