Lover

You may be looking for Liver.

Son of Mine noted that Joan Redfern and John Smith were lovers. (TV: Human Nature)

Diane Holmes had a lover, a married man. She confided this to Owen Harper, explaining that it suited her as she felt that she was "not marriage material", that with him she was "free to do what [she] liked and [she] didn't have to cook and clean for him. (TV: Out of Time)