@Damoon That's because before the year 2012-2014 netorae was a very, VERY niche plotline in officially (meaning published, money gets put into producing it, etc) released manga, anime, etc. Like, it was underground and you had to actually look for it. Then at some point, they started actually throwing it into stories everywhere to make it more "realistic" lolz and dramatic. So now people that abhor it, which is like 90+% of people not including those with that fetish, are nervous as all hell because it's actually a trope now. So when there is something like this with a weak-willed mc and promiscuous girl as the girlfriend, the people that don't know the differences come out in droves.
The only problem I have with the people calling it ntr is that, most of the time it's actually not, or they jump the gun like they are here. For me personally, because manga and anime's don't tag things like novels do, such as betrayal, netorae, cheating etc. If I was worried about the content and wanted to get some spoilers and some asshat that doesn't know the difference, claims it's netorae "vibes" but nothing happens, there is a chance I and some others may drop it when in actuality, nothing of the sort happened.