In Ohio, courts have held that an action in unjust enrichment lies when one party retains money or things of value which in justice and equity belong to another.  In Knotts v. Flynn, the court opined that where a gift is given with a mutual understanding that the parties would be married and the gift would benefit the marriage, then if the parties do not marry, unjust enrichment requires the gift be returned.[1]

In Phillips v. Newsome, the court held that the engagement ring must be returned to the donor upon termination of the engagement regardless of fault, in the absence of an agreement between the parties to the contrary.[2]

[1] Knotts v. Flynn, 1998 Ohio App. LEXIS 786 (Ohio Ct. App., Tuscarawas County Jan. 22, 1998)

[2] Phillips v. Newsome, 1990 Ohio App. LEXIS 1553 (Ohio Ct. App., Cuyahoga County Apr. 19, 1990)