Low self esteem or just crazy?

I have a friend who I am very much in love with, but I have kept it to myself because she has told me she is still in love with her ex. I ask why? She was with him for three years, and she finally caught him sleeping with another woman when she came home from work. She said most of those three years she and him basically slept in seperate bed rooms, because he was getting his physical needs met on the side. She broke up 6 months ago, and I can understand how she can still be hurt from it and not wont to date or have a relationship.

What I cant understand is how can someone who was treated so badly still be in love with someone? I compare it to a woman that gets hit by her bf and yet still stays with him. Why!!!
Low self esteem? What causes this?

many woman dig this treatment. is called "bad boy syndrome". they lust for guys that are self centered and aloof to others feelings so they become the chaser not the one being persued. many psychologist link this with thier childhood memories of parenting. usually these guys are fighters that physically protect them against others which is a turn on to keep them clingy to macho man image of him. low self esteem of course is the drive for them to want to love them and overlook their faults. they will veer away from nice guys that treat them well and respectfully.