It’s not for everyone. Specifically, sexual monogamy is not normal.
Clearly, serial sexual monogamy is the socially accepted norm in western society, but that norm has been gradually weakening for decades. In a 2016 poll, only 56% of Americans claimed to want a completely monogamous relationship. Why?
Some statistics: About 62% of marriages end in divorce. Also 60% of men and 50% of women admit to having extra-marital affairs. Despite the fact that actual sexual monogamy is present (on average) in about half of marriages, only about one in four marriages end due to marital infidelity. This suggest that non-monogamy also goes unnoticed, is tolerated or is consensual in the about 40% of all other marriages.2
How is that possible? How can the demands of western cultural norms be so far from the reality that exists behind closed doors? It turns out that western culture is indeed the exception rather than the rule, but it’s our views on monogamy that are out of the ordinary, not our tendency to live outside it.
Humans are naturally non-monogamous. Researchers have found that sexual monogamy is practiced by only a few dozen out of four thousand mammal species and in human cultures only 43 out of 238 societies practice monogamy.1 According to genetic studies, monogamy only became prevalent in human populations 10,000 years ago. Human beings are clearly evolved for multiple simultaneous sexual relationships.
The Americans abandoning monogamy in full view of the public do so not as a deviation from their nature, but as a return toward it. I suspect it is also, at least in part, a laudable rejection of the inherent dishonesty necessary to maintain secret affairs.
Some will disagree. Particularly, those in the religious right will (and do) vilify and castigate anyone who dares step out of the sanctified (or just sanctimonious) one-man-one-woman atomic family model. But the evidence we have is not at all on their side of the argument.
References
1 Barker, Meg and Langdridge, Darren (2010). Whatever happened to non-monogamies? Critical reflections on recent research and theory. Sexualities, 13(6) pp. 748–772.
2 One quarter of the 62% of marriages that fail is about 15%. Subtracting that from the average of men and women admitting affairs (55%) yields an infidelity figure of approximately 40% in the remaining (successful and non-successful) marriages.
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