Been there, done that... Had to rebuild my life afterward. Now I am in a good, happy relationship.
It is the emotional blackmail which keeps one in a relationship, even if you know it is bad for you. My bad relationship was psychological abuse, it lead to a breakdown, which took a long time to recover from.
I was lucky, my brother was rushed to hospital and I went to visit him, I got an ear bashing about not caring about my girlfriend, when I rang her on the way back to my place and couldn't reach her, so I left a voicemail (23:30). She rang back at 3 in the morning to rant at me about being uncaring.
She said, "you don't care about me."
After the stress of the relationship, which I knew was destructive and then having to deal with my brother nearly dieing, I said, "you know what? You are right!" Hung up, disconnected the telephone and switched off my mobile and managed to get a decent nights sleep.
The next morning, my mother said "welcome back." I looked much better and was more my old self.
Some people just don't get that kick back into reality and for those that are suffering physical abuse, I should think the situation is much worse.