Cactus Flower (1969)

Toni Simmons believes that the only reason her married lover won't leave his wife is because of the children. Actually, her lover, dentist Julian Winston, doesn't have any children. In fact, he doesn't even have a wife--he just tells women he does to avoid getting involved. When Julian does decide to take the plunge with Toni, she insists on meeting the first wife and Julian enlists the aid of his long-time nurse/receptionist Stephanie Dickinson to play the part.