Anyone recall a series called something like Three Dog Night?
Xander, who is attracted to Spike, is reading one of Giles' tomes on demon sexuality, male demon sexuality. Spike sees him at this and says he'll teach Xander how to get the guy he wants. And then there's lots of "I want him but he's not interested in me" before the finally become a couple.
And found it: Skuzzbopper's Three Dog Night series