I don't want to get into a nature vs nurture debate, but while I agree to some degree that part of it is biological, I think for the most part, how men feel about women, and the kind of relationships we are expected to see as normal, is completely socially constructed.
But, if you're going to bring up examples from nature, let's look at the number of animals that are actually lifelong mates who stay sexually monogamous: only 3-5%!
And actually, your biological theory doesn't really work since from an evolutionary standpoint, you want to spread your seed as much as possible. Instead, monogamy requires an individual to invest its entire reproductive potential on a single mate.
Polyamory is actually more "natural" if you want to look at it from an evolutionary perspective. (I put natural in quotes because the whole concept of "natural" or "normal" sexual behaviour and relationships is entirely socially constructed).