Is there any way to convince my best friend that her getting back together with an ex isn't a great idea?

I absolutely love my best friend, but sometimes she isn't the most logical person in the world. Most of the time actually, her logic seems completely absent especially when it comes to relationships. Anyways, I was recently really happy when she broke up with her last emotionally abusive boyfriend (who obviously was just using her as a human toy), but now she's gotten back together with an ex-boyfriend that cheated on her before, with another one of her best friends. He's even worse, in my opinion. The boyfriend also tried to pressure her into doing physical things while she was with the other boyfriend, and he's also extremely creepy and stalker-esque to me and everything else with a , but me especially. She, however, cried to me that he's changed and that she needs him. What can I do to get her to listen to me? I honestly know that he's kind of a bad person, and that he'd be an even worse boyfriend.