Hon, I think the only thing for you to do is go to whatever parties you want with whomever you want, and forget that this guy's nutty azz even exists. He has spies watching you?! You SO don't need that; I wouldn't even bother with him at all -- maybe a polite "Hi" and that's it. Don't ask him about his girl situation, and don't watch him out of the corner of your eye to see what he's doing. Just go, have fun, and don't worry about it or him. You don't need the drama.
Good luck, and let us know how it goes!
