From Wikipedia:
Mistress is a 1987 television film written by Joyce Eliason and starring Victoria Principal as Rae Colton, a beautiful woman in her middle thirties who is having an affair with a rich, married man named Wyn Brooks (Don Murray).
why you should riff it:
1. Mary Jo and Bridget can have a ball with the Knots Landing/Dallas references.
2. Rae's best friend Margo's clothes.
3. the fact at thirty-something these women thought their lives were over and all they could be were mistresses.