seojin is such an enormous exception to him that yoonhee cannot wrap his head around it. he's been sheltered his whole life and treats everyone the same and so he doesn't realise his own feelings. he has stated multiple times that he doesn't care whether seojin dies and yet subconsciously he obviously doesn't want him to. on the surface he sees seojin as just an object he wants to possess and nothing more which stems from both his emotionally stunted upbringing. his family legitimately raised themselves a sociopath.

It is funny but sad at the same time because Yoonhee really tried his best to keep Seojin alive he do things that he usually wont do (carrying someone on his back...)