"Faith and Buffy are in the library getting all sweaty." Well, first of all, Faith asks Buffy to the Homecoming dance. Which makes her feelings pretty clear. And as Mr Trick points out, "Wherever one is, you'll find the other." Obviously vampires are perceptive creatures. We can tell from this comment that they're together a lot. It's interesting that she chooses this time to tell Angel they can't be together any more. She says it's because of Scott, but it coincides nicely with Faith's arrival. She's the real reason. Buffy's falling in love again, with someone else. When B gets in the limo, she immediately notices Faith's absence. (OK, so there were supposed to be two people, but still.) Meanwhile, Faith at the dance is also wondering where B is. When she sees Scott with his date, she's immediately incensed. Anyone who hurts her girl gets what they deserve. And I think that STD allusion killed off anything between Scott and his date. When Buffy does finally arrive, Faith looks very concerned.