How do you stop thinking about an ex?

So, I broke up with my ex a few months ago(I also haven't seen her in that long), because she was cheating on me. We're kind of still friends though. Her new bf is the super jealous/controlling type that doesn't like her having any other male friends, never lets her out of his sight, etc. Since we're still friends, I want to hang out with her, but without him, but she keeps coming up with bullshit excuses to either not hang out or do it with him around. So, I just want to forget about her, but can't for some reason. She was really the first girl I actually "fell in love with"(or I think so), and I lost my v-card to her(which I now regret), so that's probably why I can't. Now it should be easy though, because not only is she a cheating slut but a gold-digger/user as well, completely rude/inconsiderate sometimes(no consideration for others), and unintelligent(she's a 20 year old high school drop-out without even a g.e.d). Basically the only good thing about her are her looks, so it should be easy to forget about her, but for some reason, I can't.