I've seen NTR in hentai as a sort of "ignore the context and look at the visuals" type of deal. Reading this manga out of curiosity, since I'd never paid attention to story or dialogue in this kind of thing.
It was interesting how the author was playing with the emotions around cheating. It makes you feel like the teacher guy, like you can't really trust this girl and you know it.
But this whole thing of her getting drugged... Yeah that was weird as hell. Him walking in on a major crime taking place, someone he cares about being actively sexually assaulted.. and his reaction is to fuck her.. Well fine, I guess.. but I went right back to "ignore the context and look at the visuals". I get that the teacher has lost his mind at this point... but the events taking place aren't cute or romantic.. It was quite sick, all of that. And their casual conversation with the culprits.. just whaaat...
Then again, the other characters in this story basically all acted insane, I just wasn't taking them seriously.
But this is what I got from paying a little bit of attention to what's being written.. a story about a series of bad decisions, culminating in a gradual loss of sanity which ultimately leads to the disastrous decision of marrying. Even her mom is ok with being a whore. It's all so gross actually.. oof.