I'm guessing it has something to do with indoctrination at a very young age. Aren't we all raised to be monogamous?

I've been reading up on the topic and it seems like one of our close cousins are the bonobos and they are not monogamous. It seems like monogamy was a social construct created by man, mostly for religious purposes so men would know who fathered their child, but I'm guessing there must be more to it than that.

I have seen women show a vehement disdain for "cheaters", but why is it so much easier for a man to accept fooling around than a woman?

Why are some of us so possessive and unwilling to share?

Are we afraid of the competition?