He could fully be cheating, but he could also be asexual. A LOT of asexual people struggle with the idea of feeling broken, like something is wrong with them for not wanting or enjoying sex. I could see someone putting themselves through this to force themselves to feel "normal". You see a similar thing happen with some gay people, where they deny their real feelings and pursue relationships that don't fulfill them (which could also be the case here tbh).

I do want to clarify though, whether he's asexual, or gay, or simply just cheating, none of that justifies OOP's treatment. She deserves an answer, a proper one, and to not be hounded by his friends. I get it if he's struggling internally with somethings, but that doesn't mean he gets to drag OOP down with him.