Tw: sexual assault

So I was messing around with this guy for a bit and he happens to be my new guys friend right? Well one day he tried to get naughty and touch me and I said no so he told me "you're gonna let me touch you or I'm gonna fuck you. I get what I want" and he drug me to his car. So I kept saying no and trying to leave but i couldn't and he started trying to take my clothes off so i got scared and finally gave up and let him touch me. Needless to say he scared the fuck out of me and I dont wanna be around him anymore but my bf likes hanging out with him. So I need advice on how to tell him what happened without him freaking out and killing this dude bc I dont want him to go to jail over a punk. Any advice?