This is a fic that was on the old Geocities BtVSSlash site, and I never bookmarked it. It's been a few years since Sunnydale and somehow Xander and Spike meet up, but there is something wrong with Spike; I can't remember if he is souled and guilt angsting or what. Spike ends up spending a weekend with Xander and then disappears, I think when Xander tries to get him to talk. The one main scene I remember is Xander talking to a gay friend of his about it at this house that they are building together. Then Spike comes back after a couple of weeks?
Sorry it's not much to go on - I'm searching the site as we speak but I'm hoping someone can point me in the right direction. :)
EDIT: Found it myself! Midnight at LAX