Anything with Mycroft observing Sherlock heavily pining over John over the years and never falling out of love, no matter if John is close or not. Others may suspect (after all, some people think John and Sherlock are/were a couple), but Mycroft sees the actual situation in detail.
I prefer unrequited love, but it can end happily with John and Sherlock getting together as lovers. No Sherlock with others, please (I just don't understand stories where Sherlock is unhappily in love with John, but, out of he blue, absolutely needing to start a relationship (temporal or otherwise, for sex or comfort or whatever) with another person/people while he's been okay on his own, "married to his Work", without this kind of relationships before falling in love, thank you very much).
John/Sherlock (possibly unrequited). Angst. Mycroft sees more than everybody else (as usual).
I prefer unrequited love, but it can end happily with John and Sherlock getting together as lovers. No Sherlock with others, please (I just don't understand stories where Sherlock is unhappily in love with John, but, out of he blue, absolutely needing to start a relationship (temporal or otherwise, for sex or comfort or whatever) with another person/people while he's been okay on his own, "married to his Work", without this kind of relationships before falling in love, thank you very much).