Here's an interesting fact that you might not have known. When an engagement is broken, deciding who keeps an engagement ring can become a legal battle. The way the ring is distributed depends on how the court looks at the case. To view the ring as a gift, the giver must have intended it to be a gift, must have given the ring to the other party as a gift and the receiver must have accepted the gift. In most cases, even though the engagement doesn't proceed, the ring stays with the receiver since it was a gift.
The problem may come with some courts when they determine that the ring is a conditional gift. A conditional gift is based on the idea that the gift is only meant to be given if certain terms are met. If the agreed on action -- in this case, a wedding -- doesn't happen, the court could rule that the ring was conditional and give it back to the giver.