Let's look at the construct of monogamy. At the very least, we can say that monogamy is the current cultural norm. Relationships that consist of non-monogamous pairings of more than two partners are all lumped under the category "alternative." But why?
Drs. Christopher Ryan and Cacilda Jetha explain in their book Sex at Dawn: The Prehistoric Origins of Modern Sexuality that monogamy became a pervasive status quo right around the agricultural revolution. Before farming, there was no such thing as land ownership; humans lived in hunter-gatherer societies, and while careful mate selection and pairbonding still occurred, children were more or less raised in a communal setting as the whole tribe was somewhat invested in a child's survival. When food (i.e., valuable goods) could be cultivated on a piece of land rather than hunted or gathered, having land became paramount. Monogamy became important because a man with valuable assets to his name (i.e. land) wanted to ensure that the children who would inherit this precious birthright were actually his. Ergo, like land, a wife became synonymous with property. Thus began our culture of ownership in a traditional nuclear marriage. And with that came the double standard of the shaming of adulterous women. Yes, farming is to blame for why we have a slut-shaming/stud-praising culture today.
Dr. Helen Fisher in her book The Anatomy of Love: The Mysteries of Mating, Marriage, and Why We Stray points out that the Oxford English Dictionary defines monogamy as "the condition, rule, or custom of being married to only one person at a time," but does not necessitate sexual fidelity. Moreover, it certainly does not suggest a lifelong partnership, as indicated by the phrase "one person at a time." Dr. Fisher goes on to note that several zoologists define monogamy even somewhat more loosely, as "a prolonged association and essentially exclusive mating relationship."
What does that mean? To me, it says that monogamy and fidelity are not mutually inclusive. Even in the wild, mammals in monogamous, pairbonded relationships still often mate with mammals other than their partner. Polygamy is practically built into our biological systems, both as males and females. For males, justifying cheating is simple: men are programmed to procreate with as many genetically fit females as possible. With females, it may be a bit more complicated, but women still have their reasons. One must admit that marriage as an institution was designed to be entered into before the peak of our reproductive years (which is usually less than a third of the way into our entire lifespans) and that it is unrealistic for us to believe that we will want to stay sexually faithful to just one person. Our brain chemistry is designed to stop releasing happy love chemicals for a partner a few years into a relationship, so divorce becomes a trend after about four years of marriage. I've been in monogamous relationships and in non-monogamous relationships, and in my experience, getting to be sexually intimate with an outside partner that I wanted was far less damaging to my relationship than not acting on my physical desires.
Finding a partner who believes in this philosophy (and actually lives it) might be difficult. Society has instilled in us the need to be possessive and "claim our property". If something will only work if it's working for both people, it becomes necessary not to try to fit two people into the same box but rather to design a relationship that is tailored to the needs of both individuals. Some say that people's needs are never in conflict, only their strategies getting them met. Let's change this antiquated style of living and not be our own oppressors. Out with the traditional, in with what's taboo.