hooked up with ex bff’s boyfriend?

disclaimer: everyone mentioned in this story is a high school senior.

my friend had a party at her house last night and I went. we drank, smoked a little ~green substance~, the whole shebang, but I ended up having sex with J.

around july, me and my best friend M got in a big fight and we haven’t really spoken since but things have calmed down between us, we’re pretty civil, friendly even. but naturally we don’t follow each other on anything and her and J had a pretty tumultuous relationship, he cheated on her before, they fought a lot, etc. but I didn’t know they had gotten back together! and J and I have a history, we’ve sexted, done oral, and handjobs but never full on sex.

so back to the party, it’s pretty obvious, J and I finally sealed the deal, someone told M that they saw J and I making out and going into a room, now M is mad at ME but is still with J? I told her many times I didn’t know they were dating, and it’s not like J said shit, so why is she only mad at me when it was an honest, drunken mistake that I sincerely apologized for? J knew he was cheating.