Personally speaking Mr. Recycle-Guy (Captain Planet), I think that girl you want actually wants to f*ck you. Mutual friends say she does, she questions you about other damsels you conquer (in tthe spirit of competition), and she wants you to met her new boyfriend - that's not natural. Regardless of whether or not you actually like her or just want to screw her, and regardless of whatever perception of depth anyone might have about her new relationship, I say screw her anyway. Gut her properly. If you decide to keep her, good, it's always wonderful to have a thing with a friend. If you decide you've exhausted your curiosity after a couple of smashes, then so be it. Don't be defensive. It's YOUR world, she's just paying rent in it. Do what your penis wants to do, then think later.