Seeing how people react I personally would add NTR just to increase the traffic of visits, whether you like it or not is not important, what matters is that people talk and are passionate about it.
Now the "girlfriend" of which the MC lost all memory and that we interacted with her once, seeing people get so upset about infidelity for me is crazy, this character of the "girlfriend" we did not have any significant relationship more than the title of "girlfriend".
How are so many people so mechanical to react? seriously who cares about a "girlfriend" who you forgot all relationship?