My ex boyfriend of one week fucked my Bestfriend

So today at school I found out that my Bestfriend fucked my ex bf of 4 months and that she said she wanted to get "back at me" because someone told her I fucked her ex which I didn't I literally only have talked to him twice and so she fucked him and sent videos to this girl who's my friend and said round 1 and just finished round 2 and sent her a video of him eating her out so I blocked them both but i told them to go fuck themself and idk what to do?? Help we've only been broken up for a week and he's already kissed like 6 people and fucked 4 other girls