I need help for my friend

My friend is in an emotionally abusive relationship. I've tried to help her more times than I can count to get out of it but he's lowered her self esteem that much that she tries to kill herself or hurt herself until she takes him back. She has depression and anxiety and he blames her for everything. Says it's her fault he's meeting other girls behind her back, it's her fault he's lost all his friends ( even though it's his own destructive behaviour that caused this) and many other things, shaming her calling her a slut, comparing her to his ex. She just now told me she's willing to take it al from him just so that he stays with her. He's 18and she is only 15. I'm 17 and I have no clue on to how I can help her out of his. I feel helpless to her because everything I suggest she shoots me down. I was abused myself physically and mentally so I know how toxic and painful it is. I just need some good advice on where to go with this