NTR is a complicated genre, but it needs to be said that a sexual relationship with the woman being stolen away is not a prerequisite. Even romantic feelings are not a prerequisite. After all, the genre is shot through with childhood friends and mothers being stolen away. The focus is on the illicit sex, not the breaking of a relationship. Sometimes it is just the shattering of an image that the protagonist had of a beloved figure. Sometimes the protagonist doesn't discover it at all. Many times the emotional turmoil at the heart of the story is experienced by the woman herself as her own self-image is shattered by her illicit sexual experiences. I'm not sure that the genre always translates very well outside of Japanese or other similar Asian cultures. There are things in western cultures that are merely distasteful that in Asian cultures are deeply disgraceful. Finding that an unworthy person is having sex with your mother is not just an embarrassment, it is a blow to your self-worth and the prospects of your family as a whole.
These are just my thoughts on the ongoing debate. I wish that I could articulate them better or had a better grasp on the terminology but I am only familiar with these concepts through travel and conversation, not being an actual representative of these cultures or a formal student of them. If there are members of Asian cultures on the board, I would invite them to clarify or correct any misapprehensions.
