From this engagement ring site:
“Regardless of who may have precipitated the end of the relationship, the question of who gets the engagement ring is not as clear-cut as it may seem. As the price of engagement rings rises, they become not only treasured tokens of love and affection, but also a significant financial investment. Because of this, the couple needs to collaborate on disposing of the ring when an engagement ends.
While every couple’s situation is different, general guidelines and etiquette for the engagement ring in regards to a severed relationship are as follows:
* First and foremost, the ring is returned to whomever purchased it, generally to the man.
* If the man does not wish the ring to be returned, the woman may keep it or dispose of it as she sees fit.
* Heirloom rings are invariably returned to the family of origin, regardless of who proposed to whom or who wears the ring.
* If the couple purchased the ring together using joint funds, the ring should be returned or sold and the money split proportionally based on the original collaboration of funds.
Some states have precise laws about the status of the ring in a broken engagement: the woman may keep it as a gift or may be required to return it on the basis of a bad faith agreement, or returning the ring may depend on who is responsible for terminating the engagement. If there is a conflict over the dispensation of the ring, it is wise to consult an attorney about local laws and precedents. For very expensive and valuable rings, a prenuptial agreement may note what should happen to the token in case of a split either before or after the wedding.”