Men and women both have dual mating strategies

Men and women both have dual mating strategies when they are able to do so

The man's dual mating strategy has a primary strategy of finding quality woman or handful of women to give his parental, provisional, protectional and associative status to as his wife (read: parenting partner), if she is high enough quality. Then his secondary strategy is to just have as much random sex with as large of a variety of women as he can that he puts no investment into

The woman's dual mating strategy has a secondary strategy to find a quality man to have children with (good genetics) and attempt to get his commitment, at least enough to be one of his partners he puts parental, provisional, protectional and associative status into.

However, that is statistically unlikely to happen. A woman's primary sexual strategy is to use one man for his genetics, then use another man for his provisioning.

This is why the female to male reproductive ratio is 17:1 during the last 8000 years (according to geneticists) even though we're also a pairboding species. ( In more recent history, as a global average, about four or five women reproduced for every one man. ) Source

It's also why women show more attraction to high testosterone indicating males (thick jaw lines) while they are ovulating, and lower testosterone indicating males (thin jaw line) when they are not.

Women evolved this way, because it is both a personally beneficial adaptation but more importantly, it was beneficial for the species as a whole. The strong/smart got to breed more, the weak got to breed less, while all children get provisioning, protection and parental investment from at least one man.

Men and women cheating (if they can) are just following their biological drives, even though they are counter-productive to social stability and familial stability. Without a framework to deter human behavior (religion, wisdom, ethics, laws) we fall back on our animalistic defaults.

All you can do is keep women at arm's length as much as possible, to keep their behavior as good as possible.