Re #6: Yeah, but she isn't the one who is breaking the promise to get married! He did! I'm a law student, and there is no consensus amongst courts as to what to do when an engagement is broken off. Some jurisdictions say that no matter what, the man gets the ring back since he bought it. Others say the one who didn't break off the engagement, is the one who keeps the ring, since it was a gift conditioned on a marriage occurring. Other courts say it's an inter vivos gift made to the woman and doesn't have to be returned.
I say do the research and find out what your jurisdiction says. If they say you can keep the ring, I say screw him and keep it/pawn it. Furthermore, I believe the Emily Post approach is if you are a girl who breaks off an engagement, you return the ring. If he breaks it off, you keep the ring. Why make his life any easier? Sell the damn thing and treat yourself to a vacation so you can forget that loser.
With time, you'll see he did you a huge favor that he revealed his true nature now, instead of down the line. I wish you the best of luck. God bless.