I usually liked all kinds of hentai doujinshi(Vanilla - NTR ) and I was practically numb to all of it without feeling much except for pleasure. Though some time ago, I recently re-read netoraserare and finally dwelled on the deeper meanings of it, On how a sexual fetish can affect someones life in a negative way. So now when I read vanilla manga/hentai, I can't get all these negative NTR/Typed(Mind-break,rape,drugs,blackmail that make you feel helpless if it happened to your relationship) thoughts out of my head and i'm not sure what to do. These thoughts use to be non-existent because I just dwelled on good art and some times plot, However I sorta started to like NTR doujinshi(netori) just for what it was( thought it still needed to have a good art) And it somehow became another one of my fetishes but then I accidently self-inserted myself as the one being ntr'd and it felt unpleasant much to say the least , not the anger and jealously people feel when they read ntr as the Boyfriend or Husband's point of view but I just felt helpless and depressed at the thought of how all these things can happen behind their back and ruin what used to be a perfectly good relationship. Now, these thoughts of " What if..." pop up when I read regular romance manga and it's really unpleasant and now it's hard to enjoy the usual fluffy romantic manga. I'm not sure if the right choice would be to try to cast all those thoughts away or just leave them there or possibly put up a indifferent type of attitude towards them.
tl;dr - You accepted Netorare as a fetish to some extent but because you feel for the guy getting cucked you get depressed when reading vanilla because you do "What if" scenarios in your head where one party cheats on the other.
You've got to remember: fiction =/= reality.
In reality someone wouldn't be that easily swayed to ride someone else's dong for sexual gratification if they were happy. If she's willing to cheat on the dude she's with, then the relationship was already in trouble. It's scummy, but it happens.
A rape victim wouldn't go back for more (though human stupidity dictates some probably have, humans are weird) and if they were drugged it would likely be something to put them to sleep, not get them aroused. Blackmail is a tricky one, but I don't think it's ever ended up with the girl being a slave to the guy's cock, certainly not willingly after any amount of time, but it has ended up with the victim commiting suicide.
NTR exists as a fetish for those who like the idea of "claiming" a woman sexually who is in a relationship. The idea is to self-insert yourself into the guy doing the cucking. Though there are the weirdos that like being cucked, and more power to them I guess.