Some people really struggle to be monogamous and experts say it's because it's not natural.
Franklin Porter, Ph.D., a couples' therapist explains, "From an evolutionary standpoint, men are wired to impregnate multiple women to further the species." Over time, people began forming families even though their instincts to get with whoever they wanted still remained.
Rebecca Hendrix, another couples' therapist adds, "As human beings we have a deep desire to matter to someone else, to know if we reach out for them they are there for us." So in exchange for someone caring, we give up the rush of being with someone new.