Andrea
I don't know who's idea it was. Faith just told me that she'd be home late and not to wait up. I didn't find out about her slaying with Buffy until I actually asked. But given that the vibe I've gotten from Buffy about Faith seems like indifference at best, I'm guessing it probably wasn't Buffy's idea.
Buffy isn't sure. She's just noticed off behavior, and I...noticed, but I didn't want to notice, so I shrugged it off. Faith says it's just all the talk of the May this guy she used to work for, and since I know the issues she has with him it's not entirely unreasonable that reminders of him would throw her off a little.
Honestly, if she wasn't still wearing that consecrated cross I got her, I'd have already done the trap-and-Latin routine on her. But she is, so I have no idea what's up.
I've given up trying to guess what Buffy's thinking, so I couldn't tell you what she thinks is up. Personally, I have no clue, and that really bugs me. I know she isn't all of a sudden regressing, she's not that girl anymore, but I can't figure out what else could be up, either. It worries the hell out of me.