My (17nb) girlfriend (17f) have been having a lot of arguments recently and they mainly revolve around this one guy.

My girlfriend used to talk to this guy while we were dating and of course that was fine by me because girls and guys can of course be friends. However, I didn't feel easy with this friendship when he proclaimed his love towards her, having full knowledge that I am with her.

He has also said to my girlfriend "I bet I could bang him out", (bang out as in beat up) and I was immensely uncomfortable with that too, so I asked her if she could cut off all forms of contact with him, and she did so happily.

Recently he's been interacting with her again and it's made me feel uneasy given the fact that he crossed that boundary that me and my girlfriend put in place with him.

She wants to be friends with him because he isn't necessarily a bad guy he's just "influenced by his friend group", and I politely told her I would be uncomfortable with her being friends with him. She knows I do not wish to control her in any way, she is friends with multiple guys, it's just this one guy in particular that keeps cropping up in arguments.

AITAH?