You may feel responsibility to call the police, but that won't do her any good if she denies everything. I'd tell her friends. So what if she made you promise not to say anything? She's freaking ashamed of him. If it's shame that helps her get out of that, so be it. Hand her over to the women to help her. Some may have been in the same situation. Regardless, they'll know more about emotions and feelings more than you do.

Honestly? I was in the same boat when I was 18. I "loved" my BF even though he did that shit to me. Still, I hated my friends because my pride took over and I didn't want to admit that they were right and I needed to get out. I resented them and alienated myself from them because all I kept hearing was "You need to do this..." and "You should do this..." I'm the kind of person who doesn't like being told what to do.

Eventually I came around and I got out of that abusive relationship. I couldn't rely on others to do it for me. It was something I had to do for myself.