My friends boyfriend..?

okay so my bestfriend was going out with this guy about a month ago who isnt a very nice guy. He was in a gang, and im guessing he still is. He gets drunk every weekend, has a gun, does every kind of drug (pretty much). Up till the starting of grade nine my friend hadnt even kissed a guy ( where in grade nine still )before, but her boyfriend peer presured her into having with him. I was definetly scared she might have a disease from him because he has had with 18 differnt girls. The worst part of it all she didnt tell me or any of her other 4 close friends. We found out from other people around the school, and after her lying about it several times she finally owned up to it. She also used to ditch us all the time for her boyfriend.. and now after being broken up for a month they got back together yesterday. I really dont think she should be going out with him, i care about her and so do my friends and he really isnt a nice guy. He told the whole school that my friend was a "screamer" in bed, and how drunk he got her. He calls her and lg and a brat, which i beleive just makes her do more stuff. She had tryed drugs and get drunk now... all because of her boyfriend. I just miss my friend from the starting of grade 9. I no everybody changes and things change, but im just looking out for her and i dont want her to become what he is. She knew he was going to ask her out so she asked us if we thought it was okay, but we are her friends we cant really say no. So we said it was her decision but we didnt want to be in her life if she was going to be continuing what she has been doing. Now they are going out, and i dont no why she would ask for our advice, if she wasnt goiung to follow it. I told her that her boyfriend isnt a good guy, and that he cheats on her and stuff but she doesnt even care, he doesnt treat her right.. She is loosing her friends, and it doesnt seem like she even cares ( and we are her only friends ) ... i need advice please, what should i do ?