There is no waifu stealing nor submission to the sexual desires of another character. The sexualization of the negative emotions of the MC never truly happens and the reaction the MC has towards this doesn't fit the submission expected of the betrayed in such genres.Whether it is NTR or not depends upon exactly what NTR is to you, Neotare was explained to mee as being like the German word schadenfreude in that its a word that mean a specific emotional reaction.
schadenfreude means "happiness at the misfortune of others."
Neotare was explained to me as meaning "despair at the (romantic) loss of precious one."
This is why manga where the characters aren't dating can still be NTR, Childhood friend/highschool crush.
Because of its emotion component NTR is decided by the person being NTR'd, if a wife cheats on her husband but the husband doesn't care its not NTR, If a high schooler see their crush going out with the high school quarterback and feels "Despair" that is NTR.
Basically its the feeling of despair that makes it NTR or not.
This means in a game its largely upon individual players whether its NTR or not, does the player feel some "despair" because of it? if yes then its NTR to them.
The scene in question isn't ntr, the reactions that come from the characters do not fit with the description.