I like my friends ex. I need help on this situation!?

[Mitri F]

So one of my close friends i known since elementary was going out with this one girl, but while they were going out, he was cheating on her with a couple girls. Her friends tried to tell her but she didn't want to hear it. Then eventually he broke up with her. Day's later, I was hanging with my friends and her. When we were alone we started talking about them breaking up and stuff. When we were talking it felt like we had a connection. We started liking each other. Then one day, my friend texted her telling her that he wanted her back and that he made a mistake, but i know deep down that he could careless. She told me she wasn't going to give into anything he was telling her, but that seemed to be false too. She told me one day that she was going to think about giving him another chance, and after that i felt so blown. Like all her friends would say that i would be the best match for her right now. The crazy part is that she knows that its the truth, but she seems to still have feelings for him. Its messed up how we were both vibing with each other, then that one text from her ex (my friend) messes up what we could've started. She deserves better than that, and i still kinda like her. I know he's my friend, but what's the point of him going out with her if he's not going to be faithful. She's a really cool, down to earth, beautiful girl. And since he messes with a bunch of girls, i know the last thing he is worrying about is her. What should i do because i like her and would like to start something with her. What should i do??