It's one of the biggest "commonplaces" of Pop Evolutionary Psychology, and somewhat of more restrained "legitimate" (I reserve the right for the scare quotes) evolutionary psychology that men are from Mars and women are from Venus in terms of sexual desire, sexual drive levels, and, above all, sexual roving eyes and interest in not being fully monogamous.
Taint quite so, says research around new studies trying to finally find a "female Viagra" or equavalent. Most of the women in most of the studies, it seems, haven't lost their Jones because of kids at home, housework, or whatever. Rather, familiarity has bred, if not contempt, ennui.
And, indeed, if I were into the "just so stories" of Pop Ev Psych, I could easily make up one to explain this, that has at least as much actual scientific grounding as do most those of Pop Ev Psychers.
First, we know that, in some mammalian species, the female of the species can do more than prevent immediate womb implantation of a fertilized embryo. She can delay immediate fertilization of an egg cell by sperm inside her uterus.
Why? Why do this?
Because a better male, evolutionarily speaking, may come along.
Well, there's no proof that human females do that. But, given that in the hunter-gatherer times of the Environment of Evolutionary Adaptedness so beloved by "legit" ev psychers and Pop Ev Psych types alike (despite somewhat shaky scientific grounding), a child would be nursed until age 3, in part as a contraceptive, but that, in part because of that and in part because of the simplicity of life there, said child was ready to do a certain amount of work by age 5, why WOULDN'T women have the seven-year-itch after four years?
Further confirmation of how Pop Ev Psych is wrong? Women lie as much as men about how much sex they have. They just underreport, rather than overreport.