Why True Monogamy Only Exists in Fiction

While monogamy is still the default for humans in this reality, all monogamous relationships in this world are ENM and only true monogamy exists in genres of popular fiction. This is because ENM in this world is a biological necessity.

After 18, a woman's sole source of nutrition is semen. Getting her belly filled with cum daily - along with remaining sexually active - is how she remains healthy and keeps her immune system strong.

Men after 18 develop a blockage at the ejaculation duct that can't be opened by self-stimulation. Men need to ejaculate multiple times a day or else they'll die of blue balls after a couple days.

The reason why ENM - and to a lesser extent, polyamory - is the norm is because if two people - even if they're madly in love - fuck each other - and only each other - for a long enough time, eventually their bodies will get bored and even reject each other. This means that the woman's touch won't be enough to stimulate her partner and even if she manages to get it unblocked, his semen will have a less likelihood of being as nutritious & fertile.

It gets even worse as being constantly fucked by the same dick will cause her pussy to essentially dry up.

Although a really sucky situation, this is how its always been so the people of this reality have found ways to adapt and still have long lasting meaningful relationships.