Why is she with him even though he treats her badly?

OK. my now ex-friend is with a guy who treats her like …(it wont let me cuss)! I mean that to! he calls her a whore constantly and is always making her angry or makes her cry. and im the one who sits there and comforts her and listens to her, and then he calls and says ‘im sorry, I love you take me back.’ she says ‘YES’ EVERY -…ING-TIME I got sick of him hurting her, and told her that she could get some one better her and shes like’I love him! why do you try to break us up?! he loves me and your just mad because no guy has ever loved you, like he loves me!’ that was a stupid come back but she has told me that before. one time she was trying to get him to go to her house and hang out and he was at a friends. his friend aaron didnt wanna go unless he got ‘something’(you should know what I mean) so Colton(the guy) asked kim’will you have sex with Aaron so I can come over. Maybe you could have sex with both of us so it wont be so bad and awkward.’ I mean seriously! what the …!?!?! if there is a guy that reads would you ‘share’ your girlfriend?? would you even ask her that? she cried(but didnt break up with his sorry butt) after she got off the phone saying how lowly does he think of me? then not 30minutes later was on the phone with him AGAIN talking about this party that she wanted to go to with him. then I asked her about what he said earlier and she said ‘ he loves me a lot! cant you see what he’s willing to do to see me?! he just really wants to see me!’ that is a …ing qoute from her. so I want to know if any of you would do this for a guy, and if its a guy reading this switch it around and would you do this for a girl?? and give some insite if you can on WHY would some one dulude themselves into loving or thinkin they love someone like that.