What should I do???

So my friend is in an abusive relationship that she doesn't really want to admit to. My other friends and I have tried to talk to her about the situation and make her realize that she deserves better and that this is not okay. Her boyfriend acts like he does not care about her and always calls her a liar when she isn't. She cries every night when she's on the phone with him. For valentine's day, he decided to start a fight with her and told her she did not deserve to have a good valentine's day because it's just a normal boring day. He has also put his hands on her before and she is left with bruises and scratches. There have been way more worse situations that occurred but my other friends and I don't know what to do anymore since talking to her just doesn't work at all and she ends up running back to him. Should I report this to someone? Or does that violate our friendship? If I do report this, who do i go to? I just need help for my friend, because I hate seeing her like this.