Paramour

She spent the weekend with her paramour.

Tom is Mary's paramour.

Tom's paramour Mary studies the history of claims of telepathy.

to run away with a paramour

The seducer appeared with dauntless front, accompanied by his paramour.

They should be chaste, not lustful, nor taking paramours:

The action scenes are deafening and punchily staged by director Louis Letterier (The Transporter), though I wish he’d set more time aside to spend with Nobby, his paramour Dawn (Rebel Wilson), their shaven-headed brood, and friends

The paramouring matron left / A babe and husband both bereft;

This meant it could even call in "third party 'paramours'" and tell them to quit their paramouring.