do you agree that men are polygamous by nature?

I don't think so. Maybe this might change from culture to culture. But as far as I know, In our part of the world men are not and women are also not polygamous. But there are exceptions. I think this depends on the culture largely.

i certainly think monogamy is not the natural state for the human being. However, in years gone by, a marriage would last a life time because life expectancy was so much lower. With rising life expectency, i think there is an increasing likelyhood of breakdown. With this in mind, rather than poligamy, what we see is a type of serial monogamy

that is true. men are polygamous by nature, but are controlling their instinct because of the society.