Monogamy and the eclipse of partible paternity are post-neolithic inventions that enabled our species to scale up civilization beyond hunter-gatherer clans of 50-150 members. The invention of property required turning women into property and policing female sexuality and behavior to verify who would inherit that property. This caused humans to switch from being more bonobo-like, using sex to solve power issues, to being more chimp-like--using power and male sexual violence to distribute artificially scarce sexual resources by status in a dominance hierarchy. Essentially, to scale up civilization beyond pre-neolithic hunter gatherer clan and tribe we forced ourselves into a civilizational envelope contrary to our nature that evolved over the 97% pre-neolithic part of our history. What you call "cheating" is just natural backsliding into the nature that we evolved over all but 3% of our history.

The current mating market is a market driven by status-metering because the neolithic revolution eliminated hunter-gatherers' more matriarchal bonobo-like freedom of sexual novelty, collective clan parenting (partible paternity) and suppression of sexual inequality. Human females have greater sexual capacity than males precisely evolution designed them to mate with multiple men. Mosuo "walking marriage" and Amazon hunter-gatherer mothers warning their sons not to be jealous of their wives' lovers are part of this process. We're designed to combine pair bonding with sexual variety. The term "cheating" is an unscientific distortion of evolutionary reality.