Also, non-physical abuse is much easier for the victim to rationalize. Your husband punching you in the mouth and telling you to go get more beer? That's not something you can ignore. Someone playing passive-aggressive mind games or threatening to dump you or cry or commit suicide if you hang out with a guy they're jealous with? Not as outwardly destructive.
My ex got back together with her mentally abusive boyfriend after we broke up, and they spent over a year together. He wasn't violent, but he was a nasty asshole and despised me primarily due to jealousy. During the premier of a film I worked on, I wanted to take my ex to it. She agreed, but the day before it premiered her boyfriend began demanding that she cancel because she "wasn't allowed" to go out with me. I sent a massive rant to her, pointing out how blatantly abusive he was being. Unlike most instances of this occurring, however, she took my anger as a sign that she needed to stand up to him. We had a good time at the premier and he finally broke up with her a few months later; she took it hard, but she eventually started to see all of the signs of abuse that she had willingly ignored and got over it immediately.