I like the idea of Sherlock being demi- or asexual, so something working with that? Maybe John further probing into the relationship thing and discovering that Sherlock's personality combined with his sexuality makes it near-impossible for him to have relationships, but he'd actually sort of like one. It's not that he hates people, they're just stupid and bigoted!
Sherlock, despite his wonderful demeanour and sparkling personality, is not a man who had a lot of admirers. He had an obvious, calculating look that could make people blurt out their secrets, and strangely enough, some people didn't like that. He was also bloody handsome, making people either scared of him, in awe of him, and head-over-heels in love.
John was all three, and that scared him shitless.
Sherlock was a vengeful god and a moody cat at the same time; often distant, often annoyingly charming to get what he wants, and blissfully unaware of everything that halfway involved feelings.
John knew Sherlock would never buy him flowers (unless for a case and/or someone gave him some and Mrs. Hudson wasn't home), or possibly spend a whole evening with him alone (Lestrade or London or some sort of fire stuck to him like static cling), but John needed Sherlock.
He needed his scarf and his cases and his eyes that were so adorably impressed on the rare occasions that John says something intelligent and the way his shirts were miles too small and made every button strain against his chest and his mind and the way his voice lowered when he knew John was hurt badly and the casual Anderson abuse and the imperceptible little things that Sherlock did to make clear to John that he liked his presence with him; whether it be a cup of tea or a blanket shoved roughly around him when it was cold.
Sherlock didn't want sex, or over-the-top declarations of love, but John knew Sherlock needed him, which, after a day where Sherlock was more whiny brat then suffering genius, was always nice.
After all, Sherlock didn't hate all people, but he did tolerate John more than most, which was basically a declaration of unsaid love.
And John was content with that, for now. He'd have to be.
Leave it to John; dependable, solid John; to fall in love with one of the most unstable substances in the world.
Sherlock bloody Holmes.
