Like the NTR thing. People seem to get super emotional about it, even if it's not strictly NTR. I'm not including any "cheating" so I wouldn't want to label my story as such. But some people seem to think that NTR is the protagonist having any kind of non-exclusive relationship. With that kind of attitude though, every single relationship that the main character has ends up as a lifelong commitment. I understand that people don't like to read about breakups but can no one have just a fling? Is there no casual sex in their world?
As someone who has learned to enjoy some NTR recently, I can tell you that the enjoyment isn’t from the sex but from how funny a pathetic character can be.
I enjoy reading pathetic characters for some reason. Others like to fantasize about being the one stealing the girl… etc.
Anyway, hate from NTR stems from the fact that most people want exclusive partners since someone being stolen or even maybe just being rejected by someone you pour out emotions into is a heart wrenching experience.
It isn’t a mystery why people hate NTR, for me I still find a lot of it hard to read but I also find the emotional side of it fascinating. Everything from a girl losing her virginity and feeling soiled to hoping she can still be with the guy she initially loved despite past mistakes (I’m not talking about NTR fapping here).
Those stories leave some lingering effects of negative feelings, kind of like the ending of Old Yeller or Corpse Bride. When watching it the first time you might have a terrible experience but when you think and process it through you realize that it’s not that bad after all.
Hence, you tend to become a bit stronger when dealing with life situations and understanding the world isn’t perfect by any means and we still gotta live through it.
Anyway, back to the main topic.
What you’re writing is probably categorized as swinging, and if they decide to stay together it’s polygamy or poly something.
Poly leaves a bad taste with people because a lot of people can’t fathom the idea of someone they I’ve and want intimacy with also having that same intimacy with someone else. While there are some humans who have no problem with it, the average human will have instincts that tell them that they want the exclusivity, especially males since there is a biological drive (which can be negated for some males) to have their own offspring.
Like polyandry which is practiced where brothers share a wife in some communities in the Himalayan areas, the younger brothers are not happy, they don’t know whose kids are actually their own and at every opportunity the males try to leave. Even if it’s considered “normal” they don’t like that set up.
Trends go by averages, not exceptions, but there is usually a biological drive behind a lot of it. Although again, there are always exceptions to every rule.