HAHAHA! Someone got cheated on before getting sidelined into a life of being an incel.
Stop being such a sensitive little pussy.
NTR adds consequences for one's actions. And realism. Each of which can greatly increase the quality of a story as it unfolds.
After all, jealousy and revenge are TWO of humanity's most common threads throughout history.
The entire "OH-I-DON'T-MIND-SHARING-YOU-WITH-10,000,000-OTHER-WOMEN" thread is the least realistic, and most boring plot line imaginable.
If you don't like getting cheated on, be a better person. Your comment tells all that there needs to be said about your personality.