Disclaimer: I do not own Buffy. No profit made, no infringement intended.
Faith sits on Buffy's windowsill while Buffy sleeps, watching her intently. The irony isn't lost on her, the evil slayer watching the good slayer sleep, just as Angelus did. It's times like this that she hates the parallels. She hates understanding the feeling of desperately wanting something you can't have, that you don't deserve, so you try to destroy it instead.
At least with Angel there are the clear distinctions of good and bad, soul and soulless. Faith never knows whether she's good or bad, if her soul is still there somewhere, or it if has abandoned her in disgust.