Art. Not much to disagree with there.

But I'd also agree with REB that some married couples spend too much time looking for other partners. If your sex life is suffering from poor marital RELATIONS, then that needs to be confronted, fixed or dissolved.
I never had much respect for those who find themselves in unhappy marriages and are playing around, but never-the-less won't face the problem or change their modus-operandi. (I'm being pursued by one right now).
If you find yourself in the same boat, you may find the catalyst that fianally sets you free!

I've had years of DRAMA in both my marriage and personal relationships, so I think what you say Art about the rarity of monogamous relationships is just that. We are hard-wired for sex. I think of my younger years when I didn't have much of a brain, but raging hormones.
Alpha females meet alpha males and n'er the twain shall meet!
But along with that came bitter disappointed and many sleepless nights.

And physical attractiveness is important in the relationship, good hygiene and health. A depressed partner is not healthy. Neither is a fat one. 25 extra lbs is grounds for counselling. 50 lbs. grounds for divorce!
At my age, I'll take someone who's done with the drama and is just glad to appreciate all the good things in life, myself included....;~)