They had slept together half a dozen times at Uni, back when John was still experimenting with things; he'd also spent two months in the chemistry programme before coming to his senses and realizing he wanted something more practical.
Sherlock stuck with chemistry – stuck to men, as well, if you wanted to put it that way – but his rebellion had been going up at East London in the first place. So maybe it was all an experiment, after that.
They'd parted friends, mostly, but it was definitely a parting – Sherlock stopped coming round the house, stopped showing up in the library on Thursday nights. But Mike had been right, when he put them back in touch; it was easy between them, the way it had been at the beginning.
"All in the past, John," Sherlock said, when John worked up the nerve to mention it, six weeks into living at Baker Street. "We were different people, before. The details of our history needn't set the terms for the present."
"So you did read that Alan Watts book," John replied, grinning. Sherlock sneered but did not deny it.
John is proud of the person he's become, his service in Vietnam and the lives he's saved. But as he sits across the living room watching Sherlock's hands, he can't help thinking of before.