All you really need to know if you're not on the FH-crack (or the Power Rangers crack) is that Bridge is psychic.
Here's a secret about Xander and sex: every time, EVERY time, it's like it was that first time with Faith, because some part of him is still 18, wide-eyed and voice cracking even though, thank god, he never said "Oh my god, I'm HAVING SEX" out loud. Every time, EVERY time, he's still only not saying that out loud through a supreme act of will. It's just that now, what he's not saying out loud is "Oh my god, I'm HAVING SEX with somebody who loves me." It's probably not much of a secret, considering. But he likes to pretend.