So there: I think it was a multi-chapter fic, but I'm not sure. Xander come back to his basement room and find Spike jacking off in front of the telly. The vampire wanted to destabilize/upset him, and Xander decide that he had enough of being pushed around. He flop down next to Spike, shove off his pants and began masturbating along with Spike. I remember that he asks him 'what are we watching today?' or something like that. Spike is completely stunned and somehow they finish in a sixty nine.
I think that in the following chapters they more or less end up in a kind of strange relationship with Xander moving to a new apartment and Spike following sooner or later.
Anyway, this tells you something, please?