What should i do? my friends are all telling me different things but they are all too involved. need some help

ok my girlfriend and i have been dating for a while. we were pretty serious; i was weeks away from proposing. her and i were/are very close. im not sure what happened really. we were doing great, no big arguments or anything just the usual bickering that we all do. i think it is a good idea to mention that her and i have been through 2 miscarriages with one of them being quite recent. it seems as though after that, she felt so distant and far away, almost to say her mind was pre-occupied with other things. i thought that it was natural for her to do that and i was there for her the best i could. long story short, soon thereafter, i found out that she had been "talking" to her ex. i found out later that week that they had actually tried to have sex. she had assured me then that she couldnt do it because of the fact that she does love me and wants to be with me. being the kind of guy i am, i forgave her and told her that she abused my trust and would have to earn that back. she did agree with me, however she did not act like she really wanted to. she more or less acted like everything was fine and back the way it was. so for the next week or so she acted like things were good, but she increasingly got more and more angry and aggressive towards me both physically and emotionally. one day she decided to just leave me for the same ex. ever since then not only i, but her family and friends have been telling her that she is making a huge mistake seeing as though he is an alcoholic and abusive person who does nothing but live in his parents basement and sell drugs for a living.
she knows and has admitted to not only me, but her parents and friends, that he is NOT the right guy for her and that she is only going to end up getting hurt in the end. she still calls me everyday pouring out to me telling me she loves me and shes sorry shes doing this and she still wants to be with me. her "reasons" are that she just needs time to be with him for a little bit until she figures "something" out. it tears me apart to know what she is doing with him and knowing that he is abusive and always drunk.
the situation IS getting better, she has deleted photos of them on her facebook, but she is still in the relationship. the problem i think is that this is her first love. it seems as though hes "brainwashed" her somehow because she acts totally different when she is with him. shes taken a HUGE step backwards in her life and we are all scared for her safety.

what do i do? i try letting her know that i love her and i want to be with her, but at the same time, i dont want her to think that she can just come running back to me when she feels like it. even though she is with him, she still kisses me and holds my hand and acts as though we are together. i dont like this at all i would rather her either be with me or be with him. but its so hard because of how close her and i are and i just want to be with her. ugh... my heart is torn and broken and would just like some advice. theres more to the story but i bet youre tired of reading.

if there is any kind of advice anyone could give, please do.