By your definition, I would been a "victim" of ntr, in my youth when I had a crush on a girl that was in a relation with an abusive asshole, because I didn't get her away from him?
In the case with the aunt, Aiko and Alexander; where did it say the protag did enjoy the show? Just because a character is presented as a LI, doesn't mean that character is "your property". Whatever happen to a character in a game that can be a possible LI, could just be part of leading up to actually make that happen.
What else did you learn from the scene? aunt's husband is banging Aiko's mum, and he is possible Aiko's father".. Help understand why the aunt is treating Aiko the way she does, yet even how unjust and undeserving it is.