A little retail therapy never hurt anyone! Just make sure not to spend too much.
You're absolutely right; you don't deserve to be with someone who doesn't return your feelings. And you certainly don't deserve a liar or a hypocrite. If he acted that way towards you, I'm sure he'll act the same way towards this new girl.
I know this sounds like a bunch of bs, but there is someone out there who will treat you better. Trust me, I'm trying to convince myself the same thing. It's not easy, but I figure each day of pain will bring me one day closer to finding someone who will really appreciate me. In the meantime, it's great to come here and vent and know that other people feel the same way.
If you do see your ex, take the high road. Try to ignore him. If he does talk to you, keep it brief and simple. I'm still trying to figure out this whole breakup mess too, and it seems to me as though some guys cope by rushing into new flings or whatever, only to figure out the new girl doesn't measure up to the old one.
I'm sorry you're hurting so much, and I hope you feel better.