My ex-girlfriend didn't go out with me for very long. Our relationship lasted the best part of three months and to be honest, I was kinda glad when it was over because I knew she was a bit of a 'player,' so to speak. Anyway, we went out in secret and all the while she continued to flirt and flounce with many other boys, including my best friend. I asked her about it at the time, and she promised that it was all a joke, and that my friend thought likewise. I have recently found out that my best friend likes her, as in 'more than friends' and I'm unsure whether I should bring my opinions to light. I'm not sure if my ex still thinks of their relationship as a joke, and I don't want him getting hurt (after all, she's still flirting with other boys). Should I just leave them alone, or should I come out and tell him about what she said regarding their 'joke' relationship?

You should tell your friend what's going on. You don't want him to get hurt by her later on. It'd be best to just come out and say what's on your mind