If you go back a couple of generations and talk to women who are seniors now, they’ll assure you that the expectations of sexual fidelity were mostly a one way street.
Women were viewed as property, or at least as inferior. And holy crap, they better not cheat because he doesn’t want to be fooled into thinking someone else’s kid is his. So SHE better not cheat. Men, of course, had their dalliances. Hence the jokes about the secretary.
As far as societal construct goes, both partners bringing marital fidelity to the table is a fairly recent construct. Recent being up to interpretation of course, but a mere few generations ago, that’s sure not how it was.
Sometimes we humans are really messed up and don’t even realize it.