When is enough, is enough?

Been talking with my friend. She have a boyfriend that thinks he can get any girl he wants. They've been together for a year but this guy still seeing some other girl. I told my friend to let go and move on. All I can hear is yes I will. Then the next time we talk the same old story. It seems that she can't make up her mind and I sometimes had enough. I already said all the things that I know can make her realize that she is way more better of without that guy. I know sometimes I hurt her but I want her to hear the truth. The next thing I know she is with the same guy and spent the Christmas and New Year. Before New year, the guy made her went to their friends house a couple of hours away from the hotel that he is staying and meet some of his "girl friends". And my friend knows about this. And she is still talking with him. I just don't understand. Sorry about his rambling. I want to let it out in my mind.