Broke up with a terrible controlling/jerky boyfriend who WAS friends with my new boyfriend. New boyfriends?

best friend invites my ex to parties knowing I am not on good terms with him and my new boyfriend is not on good terms with him. He threatened to beat up my new boyfriend and obviously isn't over the fact that I have a new man in my life bc he constantly insults my new boyfriend. Should I continue to be friendly toward my boyfriends best friend and should he remain friends with her as well? And should we attend her parties? I'd rather avoid drama, but my boyfriend insists I should go but it's hard because I can't be around my jerk ex who put me down and hurt my feelings.