If you are willing to leave the "dark" out of it, the Argentinean film "Un novio para mi mujer" (A boyfriend for my wife) is about a man who wants to leave his

If you are willing to leave the "dark" out of it, the Argentinean film "Un novio para mi mujer" (A boyfriend for my wife) is about a man who wants to leave his wife and hires someone to seduce her. The film has been remade in several countries, so I guess there is a market for your idea.