My 13 year old is obsessed with this one boy?????

How do I make my daughter see that the boy she is so infatuated with is no good? She has liked him off and on for a year now. She goes out with him then breaks up with him. He is such a player and likes all the girls. The sad thing is when she breaks up with him and he sees that another boy is interested in her he begs her to take him back and she does! Ive tried talking to her but you know moms just dont know anything. how do i help her to see he is wrong for her? She keeps getting her heart broke and she is only 13!