So men can sympathize only with a loser, who has a small penis and doesn't satisfy his girlfriend? Not with a fella who gets cheated on despite doing his part well?
Being a good guy and a beta male does not mean being a loser. You and i have totally different ideas about what a beta male is. Think about Brian at Katie's corruption, he is a beta male (he is not aggressive, not rich, treats Katie like a princess etc.) and he is
not a loser.
For me there are 2 ways to write NTR;
1- A pathetic loser as a boyfriend (like you said) and no one can sympathize with him; these ones are easily forgotten.
2- A good guy, not very rich, not very strong, not a loser but still tries to do everything to make his woman happy. That is the guy we can sympathize. That is the hero i speak about.
On the other hand, if a boyfriend acts as an alpha male, have a big penis, is rich&strong, then how do you write a comic&game where he is ntr'ed? Remember, we do not speak about one time cheating; a corruption&ntr game means that the girl will stop loving her boyfriend and will belong to the alpha male.