Is OTHER wrong in the post ? POST : it's been months since this happened but i still feel really bad.

so there's this guy i was good friends with a while ago. i found out that he had been sending girls in my class unwanted sexual messages. i saw screenshots from one of my other friends and i was really upset. i confronted him about it and he said that it wasn't that bad and everyone was overreacting. i got really mad at him and stopped talking to him. i feel like a disloyal friend for not having his back in this situation but the stuff my friend showed me was really, really disgusting. AITA?