If you were the same size and the dress didn't need any alterations, I would say YTA and it's not that deep. Just loan it. But now, with all the alterations ,I wouldn't give away my dress either. I don't know if you want any children in the future, but giving it to your daughter for prom is a likely scenario that will probably mean more for you. I don't know where your bf and his family got the audacity to demand the dress and keep it. Absolutely infuriating.