Light our own fires by Blackeyedgirl
I've come to the belated realisation that Sherlock as a fandom is a huge celebration of an asexual romance (or aromance, depending on who you talk to). Regardless of that, this fic took me all the way to the end without realising that I was on the verge of tears throughout. It was only when I finished reading I noticed how irregular I was breathing. Good emotional tension.
ETA: It has of course been entirely jossed by the start of the new season. But who cares when fic is this good.