My best friend likes a real *** hole. How do I convince her she is better than this?

My friend has had this crush on this guy since new years 2013. They have sex a lot but he is a jerk to her. For example he will say things like "you mean a lot to me" than the next day he will say "we can't talk anymore." but as soon as he wants to have sex he will call her and say that he was wrong and that he likes her. This is obviously him just trying to get her in bed. And recently he has even been flirting with me! and telling me that I mean a lot to him. I told him to **** off but he still tries to talk to me. My friend told me that a few days ago he asked her to be his girlfriend, she has been waiting for him to ask for a long time. After he asked, they of course had sex, and the next day he broke up with her saying that she "means nothing to him." I told her she needs to cut him out of her life and she is better than him. she agreed with me and deleted him of of Facebook and said she will never talk to him again. But she just called me saying that she spent the night at his house last night because "what was I supposed to do? he called me." Im starting to get really irritated with her, but because I love her and watching her do this to herself is killing me. So how do I convince her that he will never change and that she needs to move on?