John and Sherlock have a competition to see who is better at sex.
Sherlock is diagnosed with a brain tumour.
DO NOT IGNORE THE TEARJERKER WARNING!!
Sherlock finds out that John is bisexual but has given up men So he decides to set him up on a series of dates.
After two weeks away, John finally texts Sherlock. He doesn't expect Sherlock to respond. He doesn't expect Sherlock to keep texting him. And he really doesn't expect things to spiral out of control so rapidly.
John’s marriage is over and he is finally back home (i.e. at Baker Street, where he belongs). Sherlock is awfully insecure and John is awfully hesitant, and they're both awkward idiots, of course, but they figure it out. Many First Times happen.
Sherlock deduces a very interesting man on the tube one day, and starts to take public transport more often. Which is, of course, just a coincidence.
No one has ever stayed with Sherlock longer than a month. At least, no human. Fortunately, John Watson isn't about to let the little things - like biohazardous experiments and the constant threat of danger - get in the way of his friendship with a very special, very brilliant man like Sherlock Holmes.