I tend to agree having been previously in an open relationship that monogamy is more social engineering than actual natural inclination, however I'm now in a monogamous relationship and that does feel natural. If Mr Kval wanders off and sows his oats elsewhere, it's not a deal breaker for me though especially as we are sometimes continents apart for months, as I'm not naturally jealous, as long as he doesn't love the other person. I would have the mother of all problems with that, but sex alone wouldn't be the thing to split us up or lessen what we have.
Neither porn nor 'erotic' literature to me has a bearing on monogamy or polygamy, that's just recreation and entirely irrelevant (and like Naomi there isn't enough money in the world to make me read 50 shades of utterly boring smut).