Biologically, men are not programmed to be monogamous.

But, we are civilized and have been Christeo-Judeo-AMDK brainwashed with Victorian values (back when the British Empire shat on more than a quarter of the known world) to rise above our base instincts and be loyal and faithful to one partner.

For those who find that their moral values align, then good for them and may they find happiness long in their marriages.

For those whose biological drive strain and push against the boundaries of civic morality and societal norms, then my commiserations.

It is what it is.

Good explanation

Again, to dissect and discern further, intimacy can be further divided into physical, emotional, mental & spiritual forms - and each subcategory will offer its own neurochemicals to batten the hatches and tie one down securely, or lack thereof to allow a free kite to fly free.

Maybe he’s asking because he wants to justify a future action?

Again, this boils down (for the most part) to biology. The female species is often "slower" to warm up, while the male species' primary aim is to sow as many oats as possible.