Seious question!?

i have this friend, and i've known her for six years now. and i hate her new boyfriend, he is a druggie and has had with two girls sence her and him started going out, he also always threatins to break up with her if she doesn't come to his house when he says too, and the worst thing is that he acually hit her. i told her he was S and wasn't worth her time, and that he will most likley become a woman beater or a rapist. she said he wouldn't do that, now they are acually talking about having a baby, she is only 15 he is turnin 17, he could end up hurting that baby if she has one. what do i do. she told me to leave it alone, i just can't. help me please.