God knows.
Some women just go back and back and back. Until eventually they are killed. 
I don't understand it. Especially not if they've got OUT! Why go back? I suppose they fall for the "I love you, I've changed, I'll never hurt you again" shit. It's really sad.
I don't understand how you could go back to someone who beat you. How you could share their bed, remembering what they did to you. Surely you'd just be waiting for the day they'll do it again?