should i leave, or stay

last friday night i got off work late and met my bf at a bar. we were having fun singing kareoke and playing pool with an older woman and her guy friend. i went to the bathroom and when i cam back the guy we had been hanging out with took me aside and told me that my bf had been sexually hitting on this older woman! i went up to her and confronted her. she admitted everything thank god. when i asked him the next morning he says he has a flirty personality and that he was being "friendly". BULLSHIT.