Don't let other people tell you what to do with it; do what you feel you personally should do.
Honestly if it were me it would probably have to do with my feelings towards the person and whether or not I want to remember them. If there are bad memories and you feel fine selling it, then go for it. But I agree with belle that if it's an engagement ring or something very expensive you should give it back if he spent lots on it. Just the respectful thing to do