Friends Boyfriend is a jerk????

My best friend since I can remember is going out with this jerky guy. Actually he is my ex.... I know he is the biggest jerk on the planet... Since he lives in my neighborhood and rides my bus. I tell my friend all the mean things he does and says to me, but it doesn't make a difference. She is still going out with him and we all hate him. I don't know what to do... I can't lose her as a friend.