My friend

This is about my friend, Brad. Brad's been like a brother to me, almost a son in some ways. Well, recently he's dating this girl (the one I told you guys called me every day). She's a habitual liar, she has no real attraction to him, she's an attention whore to the umpth degree, she only is using him to get attention, she's also using him because she knows he'll worship her, and finally because she knows he'll do whatever she wants. I can't really do much in this situation except watch. I already told him that I won't try to interfere with this relationship but to be careful because, as mentioned before, she's a habitual liar and she will put him into a world of hurt...

What really bothers me is that this is, in the end, exploitation of a very gullible and innocent person who I consider family. This girl doesn't care about any goddamn person in this world except herself. And I feel really powerless and weak. I know if I try to do anything, I'd lose a really good friend and would look like a controlling asshole. But if I don't do anything, some really nasty shit will go down...*sighs* Any comforting words, advice, etc.?