/r/AskReddit, I need some help with My girlfriend and her abusive ex. Can someone give me a suggestion on what to do?

My girlfriend and I are only freshmen in high school and we started dating more than a few weeks ago. She told me about her ex boyfriend who is an abusive piece of shit. Apparently, he confronts any new guy she takes interest in and tells them a bunch of fake shit about herpes and what not. He also passes off hurtful comments to her.He also did this to another girl he dated, in which he actually had his friends confront the boyfriend and he tried talking her back into a relationship with him. This girl has called the police and filed reports against him about abuse and what not. The police told her "Yeah, we know about him". Now, this kid is in my music theory class where I expected him to at least say something to me, he said nothing, but said something to his friend and they both looked over at me. She later told me that if he didn't say anything to me today, that's a huge thing. Now, keep in mind, I'm just a 14 year old scrawny little fuck. When I try to confront people, my words get all screwy and mixed and I stutter. If this kid wants to fight, I do not stand a single chance. I don't like to fight with fists and honestly, I just want him to leave her alone so she doesn't have to suffer. If any of you have any suggestions, please tell me. tl;dr Intimidated by girlfriend's abusive ex-boyfriend, want him to stop bothering her and me, but I feel like I can't do anything about it.