Need help and advice :(

Well things for me are going great right now. Im well on track, feeling great, got loads of energy etc. I am going to chiro for my back tomorrow hopefully as its been giving me hell, but im in such a positive frame of mind that im not even letting that really bother me too much. However I have this one big problem that is now interfering badly and I need to get it sorted so that it doesnt get me off track!!!
My baby sisters are the world to me. My whole family are very close and I would do anything for them, no matter what. My sister has been dating this guy for almost a year now and he is bad news. Ive tried to be supportive and let her make her own decisions, but it is now getting out of hand. He is very quick to get angry with her if she is seen talking to other guys, yet he still reguarly sees all of his exs, hes done time, he has a child, he does drugs... he has no money, no stability and he uses my sister. She has low self confidence, I dont know why, shes beautiful, funny, caring... but i think her confidence is one of the main reasons she is with him.
But now they are talking about moving in together and stepping things up a bit. Ive stood back until now, but now im just getting extremely frustrated. Ive tried to talk to her about it but she wont listen. It got to boiling point tonight and we had a big fight about it. Now she says that I will only push her away if I dont support her. What do I do!!! Ive tried to be supportive, ive tried to drop a few hints in there, and ive flat out told her I dont like him and that she deserves better. But I just cant stand back and watch her throw her life away with him!!!
Its got me really anxious and I want to be there for her, but I can not support her on this one. I have no idea how to tackle it. I dont want to push her away all together, but how can I make her see it. All her friends and our other family agree with me, but no one knows what to do. Help!!