You can think and believe what you want.
Then there's biology.
Biology dictates that a woman invests highly on carrying for a child and supporting it for the first few years.
A man (as most animals) has little interest in investing in a child that isn't genetically his (and you get more abuse from step fathers, and mothers, than from parents).
So it is in the interest of both sexes to raise the young together.
Because we are a social species, monogamy isn't as strong as in some other monogamous animals, and we get quite a lot of support by relatives, or close communities (often inbred to some extent).
But monogamy is a construct by neither sex exclusively.
It's both biological and cultural.
But, the sexual instinct is very strong to motivate individuals to procreate. Without it, the species would end.
And men, as women, will always be unconsciously looking for the best partner to spread their genes with.
That explains the difference between generically preferred partners for men and women. Young, fertile women for men and older, powerful men for women.
Yes, it's not as simple as that, because then we have cultural constructs and individual quirks, but we should never forget the biological and evolutionary aspects in human behaviour.