Formal Etiquette dictates that she should return the ring. Although most people won’t.
You will not get full price for the ring if you attempt to pawn it, because it’s like a car…once it leaves the lot aka the store, the price will begin to drop unless the ring adheres to the ‘traditional 4 Cs: cut, clarity, carat and color.’ The highest grade in all four categories.
PS: In some states, he could possibly sue her [if he wanted to go that far in order to retrieve the ring].
Some states have laws on the books pertaining to the promise of marriage as a verbal contract and the ring is considered personal/private property as part of the aforementioned agreement.
Depending on ‘where’ you live. My advice, always seek legal counsel for such matters.
You guys all make great points, but I actually surprisingly disagree. I dont think that the guy should ask for it back. Now if he ask for it, I will give it back, but I just think that based on the fact that he gave it to you, he shouldn’t give it back. If what you felt in the moment was genuine, then you should ask for it back.