Help me plz!!!! :p ='(?

ok so about a month or so ago my bff and her bf (sam) broke up. she dumped him cuz she started to like my bf (brendan). well i broke up with him a week later cuz we go to different schools so we never got to see eachother. so the next day i came back to school and my bff told me she was dating brendan so i was like oh thats cool. then later that day i got a note from sam (her ex). the note said some stuff and at the end of the note he wrote "will u go out with me" so i thought, well sence my friend is datin my ex then she wont mind if i date sam. so i said yes. well when she found out she freaked out and told me that we werent friends anymore and then she started all kinds of crap and drama. so one day i finnally asked her wut her problem is and asked if we wud eva be friends again and she said that it was all my fault and that if i had told sam no that we wud be friends. so its apparently ok for her to date my ex but not ok for me to date hers! IS IT REALLY MY FAULY THAT WE ARENT FRIENDS AGAIN?!