My ex and I have been in an off relationship for the past 8 years, the first 2 of which we were engaged. I kept the ring thinking every time we got back together I'd need it again at some point. I never did. Times are hard after Christmas and I'm wondering seeing as though it's not going to be needed would it be ok to sell it?
It's legally yours to sell. I would also advise checking it out with two or three different jewellers (go to high street jewellers/pawnbrokers not the online gold-buyers as you will get a much better price); also ask how much you would get if you pawned it rather than selling it outright.
Traditionally it is seen as part of a 'contract to marry' and should be returned. However most solicitors consider it to be a gift now. Don't think for a second you'll get anywhere near what it cost in the shop though (maybe pay for petrol to Cornwall rather than holiday abroad?!).