Here's a complete list of whom (what) John has murdered since he first met Sherlock:
- the cabbie,
- a curious strain of staphylococcous fleurettii growing in the agar Sherlock had been cultivating in the butter dish,
- four bees, and John never wants to know exactly what Sherlock was doing keeping them taped up under wax paper in an old boot,
- a rare African vine that was surprisingly opposed to regular watering,
- lots of maggots,
- really, lots,
- whatever was growing in that foot in the vegetable bin, which would have been a lot more reassuring if it had been maggots, and
- one lamprey.
Really, the biggest tragedy was the plant.
Sherlock's lists are all a tad more theoretical. He has quite a few, starting with "consequences thereof," leading on into "highly correlated with," "common symptoms," and so on.
There's no entry in the ICD-10 for it, but Sherlock doesn't need a clinical assessment to name his ailment. This is one area in which he feels supremely confident to self-diagnose. And it's completely wretched—
—kissing John, well, John kissing him, tender and undemanding, one hand firm on Sherlock's shoulder, the other warm and soft and curving around his hip, and Sherlock feels—
—to find that he's fallen helplessly, heedlessly, recklessly, finally in love.
Although he has compiled a thorough inventory of the evidence — of course — Sherlock's still not quite sure when he succumbed. Sometime in between the time John told him it was inappropriate to giggle at crime scenes and when he clamped his arms around Moriarty at the side of the pool, he's certain. There was no one moment, though — no piercing insight, no rapturous reveal. Just a series of things that he might easily have written off as coincidence:
- his irritation at John's poor taste in dates,
- his vexation with John's poor taste in all things sartorial,
- his inclination to feed John with cases and stakeouts and microwaved tea,
- his preoccupation with the way John's hair curls at the back of his neck when he's a week past due for a trim,
- his hesitation to rouse John, napping on the sofa, from his sleep, and
- his overwhelming hunger to touch John — an arm, a shoulder, a thigh, a wrist — to know him, all of him, every inch of him that can be given up to a careful caress.
Sherlock can't refute the evidence presented as he regards it cumulatively. Correlation. Causation. It's conclusive.
Sooner or later, things come to a head, and Sherlock finds himself saying, desperately, "Why on earth would you stay and risk everything for the chance to, to grow old together? I'm not a good person. I might murder someone for you someday. I might murder you, to keep you from leaving me."
"I've killed someone for you already," John says. His expression is neutral, his gaze level.
Sherlock sits all the way back on the sofa and remains staring at John. "You have," he says, softly.
"Yep," says John. "And I imagine I'll do it again."