Personally, if I were in Carwyns position, I wouldn't hesitate to end my relationship with Gwen so I don't disagree with you, but he does love her despite everything and I imagine most people would struggle with that. Also the situation with them being in those caves with those horny pervs would make breaking up with her awkward because Gwen would probably start fucking one of them pretty quickly. Imagine being stuck in there constantly listening to your former crush get fucked. She really shouldn't have followed Carwyn.
From Carwyn's POV, this whole situation is only happening because Gwen followed him, which he explicitly said he didn't want. So him not handling it well is kind of to be expected.
He never says no, he says not right now. He also basically gives in at the start of of the servitor levels.
Also if he's saying no in your mind, then there isn't any NTR going on and Gwen did nothing wrong right?
He's cursed to be a woman. Something Gwen already is. It's just funny to think Carwyn would give in infinitely easier then Gwen in her shoes.
Since they're on a suicide mission (as far as they know), not right now and not ever are the same thing. As far as NTR goes, I'd say that it's more about the emotions. Carwyn doesn't want Gwen to be with anyone else, even if at the start of the story he doesn't think they should be together either. And later it becomes pretty pure NTR since
As far as the curse goes, the curse is not that Carwyn turns into a woman. It will become more apparent in the next update.
It's funny cause Carwyn says he doesn't want to play with her heart and that's specifically what he does.
If he loves her then he should said yes, she clearly loves him.
And if he doesn't he clearly doesn't have the right to dictate who she can or can't be with. Being "awkward" seeing her fucking isn't a good excuse to mindfuck her/ emotionally hamstring her.
There's several routes where Carwyn says that he knew what the guys were doing but didn't actively stop it because he didn't feel it was his right to. That doesn't mean he handles it well, both of them handle the situation pretty badly.
Anyway, I'm not trying to "defend" Carwyn, just explain his emotions and actions. He does a pretty bad job handling what happens overall. I'd say the NTR scenario is about 75% his fault.