Whether you can keep your engagement ring upon divorce depends on when it was acquired.
If the engagement ring was acquired prior to the marriage, the spouse who received the ring will be entitled to keep the ring upon divorce as non-marital property, free from equitable distribution or sale by the Court.
If the ring was acquired after the marriage, its value will be marital property. Or, if the ring was upgraded during the marriage, it will be partly marital property. However, because it was a gift to one spouse, the recipient spouse is entitled to keep the ring and, therefore, the ring will not be sold upon divorce.
Keep in mind that an engagement ring is a conditional gift, conditioned on the promise to marry. Therefore, if there is no wedding, the condition for the gift has not been met and the ring should be returned.