shitty friends (how to drop them? idfk)

ok so 4 months ago. i started dating this boy. we hit it off but it wasn't anything special it was more platonic idk he clearly didnt like me much. but that's besides the point. we dated for 3 months. so not very long but that's finee. but when i broke it off with him (it's a longg story i'll save for later lolz) so like 4 days after we broke up a mutual friend and my bestfriend all made a group call with me. which isnt a big deal. but the thing about snapchat is in order to make a group call u have to make a gc. which sucks but still isnt a problem. the problem comes in the next day when our mutual friend turns the group call into a full on gc by adding every one of his friends. including my ex bf. THIS is the real problem the start of it all. later that night our mutual calls the gc me, my bstf, my ex and a few other people join, around 30mins-1hr go by and most everyone had left. other than the original 3. By that time it was pretty late so i chose to leave and go take a shower. leaving my friend, my bstf and my ex all in a call i wouldn't have thought anything of it. It was just a call. but i was fucking wrong. MY EX NOW SUDDENLY LIKES MY BESTFRIEND AND SHE LIKES HIM TOO WHAT THE FUCK. AND 2 MFING DAYS LATER THEY START DATINGG. MY EX AND BESTFRIEND. so now u can see why she's a shitty friend right. and everyone at school knew about the situation. and lemme tell u my bestfriend is known for this kinda shit so ofc everyone took my side. And that just made it harder to drop her. because schoool feeds of drama. AND everything i said to anyone got around to her. even if i said nothing it got around to her, people were just making shit up. so now i couldn't drop her bc i had put myself in this akward position :(