While I very much agree with this I have to say that you need to consider the fact that the dude has been traumatized. He witnessed at a VERY VERY young age his mother getting abused by his father. He is scared of getting involved in a situation similar to that. He thought all relationships were like that or would eventually be like that. Until he saw Dojins parents love for each other. Trauma isn't something that you just up and get over like the snap of your fingers it takes time to heal. Even if I hate his ass I can still understand and consider that much. Besides he's changing slowly but surely. Just that he doesn't realise that his feelings for dojin is not only pervy but he does love and care for him. He's a lil slow on the uptake and everything else except math.
I agree with your reasons but weren't we supposed to see that growth?. Did Fargo totally forget about giving him a closure? I mean, dojin also did not start off as a great character and heesoo too, he wasn't a good character in the start as well but i believe we have seen them change and atleast redeem for what they did. Meanwhile hyesung is still the same as he was in the beginning. I would have loved to see his trauma being addressed to and him coming to terms with his feelings. I consider it as a fault in writing of the story.
But now the story is about to end and we basically have to deal with that gap in the story. It makes me question like " is hyesung only in the marriage bcz he has a kid with dojin?" " Is he not willing to be with dojin?" Then i, as a reader think that i have to romanticise a marriage or any event that happened with the main couple just bcz the story revolves around them without being given some strong grounds to do that.
Maybe there will be closure we just have to wait for it. Also to be honest I don't expect much from most Korean nor Chinese mangas seeing as they have a tendency to romantise abusive relationships where the mac is either getting beating from their spouse, cheated on, being thoroughly humiliated then magically ending up with the same abusive partner who changes their way out of the blue or over something so stupid that you end up thinking why weren't you just nice from the beginning.
I have read mangas/ webtoons where i have disliked the mc but gradually through constant character development started loving them. But yeah i still do not like hyesung. 0 character development lol. And appreciation in a relationship doesn't always have to be sexual in nature. His attitude is very repulsive. There's a limit to how much you can hurt/ push away a person you actually like but are too scared to confront. Naaah! Hyesung needs to grow up for real.