I read this shounen-ai a really long time ago, so I can hardly remember it.... I think it was a oneshot or in an anthology.... There's a blackout of some sort during a party/gathering, and the main couple is there. The uke is the shy type with a supposedly unrequited love but he went and kissed the seme since it was pitch black and there was a girl next to him (so he would think it was the girl). The seme, however, somehow knew it was the uke and stuff happened and they had their happy ending. Sorry, but that's really all I can remember.... If you have any ideas, please help! >___<;;

I think it is the second oneshot in Shounen Tsubaki - I REALLY love the main story and the oneshots. They are all VERY good.

Edit However, this is not Shounen-ai - they don't have intercourse, but there is some 'activity' (I guess that is a good way to put it?).