Times Fool by MsJane has a scene like this, except it's in the future and so there's no Cordelia.
http://www.bloodshedverse.com/stories.php?go=chapters&no=12736Forty years after the battle in Los Angeles, Spike comes in from the cold under the impression that Buffy and Angel are involved, which was why he stayed away. Angel keeps letting him think that, until Spike smells Slayer blood on Angel and gets upset enough to drop his blas� act.