Man i want to punch Kanda for making this "misunderstanding" go on for so long. It was already established that her girlfriend doesnt care if she's a girl. She shouldve just confessed at that point.
I honestly dont like anime/manga with cheating or NTR elements but the comedy here has made it tolerable. Alongside with that, what @ninja said below about "de-humanizing" the husband character has made this manga be more of like a "netori" instead of just plain NTR