Mother Nature has programmed women into being unfaithful just as men, though in different ways.

A woman's child will ALWAYS have half her genes regardless of the father. She just needs to find a sucker to provide for her and her bastard offspring.

A man can impregnate many women, some of which may manage to rear their child / children to adulthood.

Pair bonding is also a real thing, a strategy that may deal with the hardest of times. Men are physically strong, whereas women are emotionally far stronger than men - their survival strategy (particularly over men).