That's a tricky one. If my best friend's boyfriend cheated on her for example, I think I would tell her. But from what you are saying, she seems to know the kind of guy she is with. In short, despite the complaining to you/therapist, admitting he is a jerk, the break-ups she *still* does not seem ready to ditch him for good. In this sense, the best thing might be simply to be there for her, as a friend. Until she makes up her mind as to what she wants.