moneygamy

A form of committed interpersonal relationship which is shaped more by economic constraints or objectives than by romantic attraction. For example, when one partner only sleeps with the other for money; or, when a partner can't afford a divorce from the other.

She pretends she's no golddigger but in reality she just believes in moneygamy.

He'd have to pay her millions so for now he lives a life of moneygamy.