First page of this comment section, someone mentions "yandere NTR"
They are right. People often misuse the word NTR when in fact it's just adultery (even when there is no cheating)
NTR is how the story is devolved in order to make the readers feeling bad and to put themselves in the cuckold's shoes. For anyone that cares, go read NTR hentai and you'll know what it means.
There is a difference between Cheating and NTR.