text: i am i a bad sister and person for sleeping with my sisters exboyfriend? they other day i was talking to my roommate which just happens to be my little sisters ex-boyfriend and we ended up haveing sex. i know i broke the number one rule of sisterhood but does that make me a bad sister and a bad person. i know i can never tell her or my boyfriend that it happened and i feel so guilty. on top of that i am getting jealous when she comes over to talk to him. someone please help!!!! look, if she's not dating him, tough shit. she didn't like him, he's all yours.