This is probably a dumb question given that they have separate tags on this site, but where does cheating fit in, i.e. one partner having an affair that they hope the other partner doesn't discover and does their best to keep secret? Is that rolled in under the NTR blanket somewhere? And if that affair is discovered by the wronged partner, does it then become Netorare? I should add that I am wholly unfamiliar with all anime tropes so I'm trying to figure out which tags mean what.
I think only westerners care about being noticed. In most of the Japanese NTR porn I have seen, the partner does not know that she is being cheated on until the last moment (until it is too late). Maybe doubt... But even that emerges much later.
It's basically just like Cheating.
Because if you're cheating, it will eventually come out
Let me explain briefly: In a porn that lasts 1.30/2 hours (in a story that sometimes lasts 1 month, sometimes 5-6 months, sometimes 1 year), the partner suspects that the movie has something in the 30 min-1 hour range. And in the last 10 minutes of the movie, he realizes that he has been deceived...
After that, they either divorce or forgive their partner or become a cockold.