How do you tell your friend to move on when she is still in love? -for her own good-?

To make a LONG story SHORT- my best friend fell in love a year ago with this great/funny guy_he admitted to her that he still had feelings for his ex- even though my friend %26amp; him ended up hooking up (only making out) a few times鈥?he told her that they couldn鈥檛 be official b/c he didn鈥檛 think it would be fare to her since he still had feelings for another girl- he went back to his ex twice (unofficially) After that was over he began telling my best friend how much he loved her and how he just wasn鈥檛 ready for a relationship after finally %26amp; completely getting out of his last. She understood and decided to wait. They ended up having sex. He started seeing another girl and then out of the blue- He called the new girl HIS GIRLFRIEND- they have been dating for a while now- he cheated on her with my best friend (sex)__I think that is another reason why my best friend thinks that the couple wont last very long and she should wait it out AGAIN鈥?I can鈥檛 keep seeing her like this and watching it happen over and over again鈥?She isn鈥檛 crazy- when his girlfriend isn鈥檛 there he gives my best friend a lot of attention that she doesn鈥檛 鈥榓sk鈥?for--- I understand why she thinks that if she鈥檒l stay around long enough they will end up together. Help?How do you tell your friend to move on when she is still in love? -for her own good-?
just tell your friend move on savvy ,, life is to short to rethink the same old song!!