I had a friend, now deceased, who was a counseling psychiatrist.  His name was Dr. Ron Reivich and he once told me that one of the major reasons men and women cheat on their husbands and wives is based on what he called “the mommy-daddy syndrome.”  That is, when single, young men and women are originally involved with each other they often engage in “sexually evil and wild” behavior. But after they are married and have children, they suddenly see each other in parental roles. The man might have a briefcase and goes off to work every morning and she begins to see him as “daddy.” She is involved in maternal activities with their children and he begins to see her as “mommy.”  Since one doesn’t engage in sexually wild and evil behavior with one’s own mother or father, they seek someone outside their marriage.