I always have to remind people of the difference between what some Western people think of what NTR is and what it actually is , for the people in the back, from VNDB:
"Netorare is more than a simple act of infidelity, but the fetishization of jealousy and other negative feelings commonly associated with it.
For a game to be classified as Netorare the following conditions must be met:
1. The protagonist's significant other, a very close friend, or in some cases, a close relative is stolen from him by someone seducing, coercing, blackmailing, outright raping them, or by using other techniques. It doesn't necessarily mean that they are literally stolen, but the negative feelings experienced by their significant other might make it seem so.
2. The one who loses their loved one almost always finds out about the situation and suffers from jealousy and the feeling of helplessness arisen from an inability to change anything. The one stealing the lover and/or the stolen loved one might rub it in by humiliating the loser in private or in public.
3. The trait does not apply if the character having sex with someone else does not have a close loving relationship with the protagonist, and if the protagonist does not experience jealousy and other negative feelings upon finding out about the act. In other words, the ties between the partners and their forcible separation is important to the netorare fetish. For example, an unrequited crush or a potential hero(ine) on a different route would not count for the purposes of this fetish.
4. The act of stealing must happen while the protagonist is in a relationship with the stolen significant other. Scenes of heroine's past relationships do not count as Netorare.
The game is usually portrayed from the perspective of someone losing his significant other, in order to delve deep into the jealousy aspect of the fetish, however, for story purposes the game might switch between multiple POVs and also portray the events from the perspective of the stolen SO."
So this ending is an NTR classic and faithful to the genre you may not like it but hey that's the purpose
It's like going into BDSM thinking it's just slapping ass no buddy that's cute, its about enjoying pain