best friend and best friend

I have 2 best friends who are talking and me and the guy use to be fuck buddies and she knows that. well it’s been 3 weeks since we last fucked and last night him and her weren’t texting each other but me and him were and so he came to my house and we fucked and he asked me not to tell her and of course i wouldn’t AND THEN she hung out with her ex that night and kinda disappeared for an hour soooo don’t wanna assume anything buuuttt and she asked me not to tell him BUT they both asked me to tell each other if the other does something AND NOW i’m stuck. moral of the story... don’t hook up 2 of your best friends