A happy marriage is the timeless goal, which in our days has become a very difficult matter. In modern societies characterized by multiple choices in all fields, sexual liberation, and the exaggerated egotistical traits of each of us, the maintenance and longevity of marriage and/or companionship present enormous problems. Infidelity, parallel relationships, and extramarital affairs are one of the main causes of divorce and relationship breakdown. This is the subject addressed by this book. In our lives, within the circle of acquaintances, relatives, and colleagues, there will always be desirable men, masculine, intelligent, socially and economically established. In our environment, there will always be intelligent, wealthy, young, beautiful, tender, healthy, and willing women. There will always be temptations around us, attractive propositions from willing males and females, who will attempt to boost our ego, corrupt our morals, dismantle our principles and values, and shake us erotically. At least they will try. It is up to each of us to provide our answers, whether from the position of the victim, the perpetrator, or the third person. It is no coincidence that many family counselors and psychotherapists consider marital fidelity as a form of psychotherapy, a high exercise of self-control, self-respect, self-restraint, as an indication that centuries of civilization have left their mark on mutual respect and the democratic rights of others. However, it seems again that in the clash between society and biology, the latter often emerges victorious.