I don't remember the name or the author, or what archive I found it in; but it's an established relationship story, Xander and Spike are in the hardware store in the middle of the night. Xander had surgery on his knee so Spike is being all overprotective, and the cashier (who Xander knows, of course) asks him if he knows he's with a vampire. I remember they were painting their bedroom. Does this sound familiar to anyone?