I imagine it's a lot like an abusive relationship. When you're outside one you can say "Why would she ever stay with him, he's a jerk! She should just pack up and leave!" But when someone is in a relationship and the abuse grows gradually over time, and the love gets mingled in with the abuse, it can be challenging. You might say "OK he's crossed the line. No wait, he's really sorry, I'll give him another chance." It's really hard to judge, if you've put up with X, is it really worth leaving for X + 1, when does your "real line" get crossed?