text: It was right to tell your friend he was flirting.  You also could have told him to stop or you would tell his girl and if it stopped then not have said anything  Either way what's done is done.  Don't blame yourself for their break up but I definitely would advise against going out with him.  A friends ex is always off limits unless you want to lose a friend.  Boyfriends may come and go but a true friend will always be there and you don't want to jeopardize your friendship over a man.