I’m sure that I’m going to get an earful here, but I watched the episode again and I read the scene in a different way, I still dislike Xander in this episode but… I don’t think that he manipulates Faith.
Earlier in the episode, we see Faith telling Buffy about her bad experiences with men and how she’s now “strictly get some, get gone.” I see her genuinely trying to bond with Buffy, she is clearly crass in the way she poses her questions, but she seems sincerely interested in getting to know more about Buffy and Angel, a huge chapter in the Scoobies lives pre-Faith. She’s put off by Buffy’s response but backs down.
Then Gwendolyn visits Faith in her motel room and makes her feel like the outcast again, casually mentioning the “secret” meeting between the Scoobies, asks her to trust her, compares her to the Spartans and promises to make her a better slayer.
When Faith finds Xander in The Bronze, he doesn’t want to talk, but Faith is pissed by being left out of their meeting and feels betrayed when she finds out that Buffy knew about Angel being alive. I interpret this scene as Xander speaking without thinking, repeating what he said in the meeting: Angel = dangerous, Buffy not listening, Glove in Angel’s hands = bad bad.
Once they find Giles, Xander second guesses himself instead of jumping immediately to blame Angel, but Faith’s response is “Yeah, and he's gonna have a whole lot of company (referring to Giles possibly dying), unless *I* do something permanent.”
This is the only time that I remember Faith being righteous, as opposed to cynical or pleasure seeking when referring to slaying. I read it as Faith thinking that she’s the only one who can stop Angel because Buffy is blinded by love, finally being “better” than Buffy at something and maybe making Gwendolyn proud of her.
I still agree that Xander is way out of line by confronting Buffy earlier, for not thinking twice about what he tells Faith and by going along with her until he stops to second guess himself, but I don’t see him as manipulating Faith. I see Gwendolyn as the main manipulator. She senses Faith need for belonging and praise, and the Angel angle works out in her favor.