
Keep in mind that Seo-an appears to be unable to understand people's feelings or even bothered to do so because he's far too caught up with his own desire to be recognized by his father (or to fulfill the expectation placed on him). Which is why it's understandable that he's frustrated over Woonwo's vulnerability towards his father, Seo-an may not consciously felt it, but Woonwo's inability to cut off his father is in juxtaposition to his own, and ironically Seo-an too cannot cut his own father off.
Worsen by Woonwo being the exact opposite in which he cares too much about other people's feelings, he put himself in other's shoes and tend to let himself be hurt rather than others being hurt. In turn, causing the clash between him and Seo-an hit harder.
It's lost on me why people hating Woowon? When I genuinely thought people would dislike Seo-an more, considering his temperament and control freak side. I guess you people never have an a55hole of a family you hate but can't get rid of, both Seo-an and Woonwo responses are valid.
They're actually quite the same, the way they're both not in control of their life, but one in wealth while the other not having enough.
Seo-an being the rich kid but never loved, everything he do never enough and constantly talked down. He thirst for recognition, to have something of his own, to have control, which led to his panic disorder because there he don't have the control and the ghost of his father's pressure suffocates him. It's amazing enough he could stand in front of his father given his condition. When Woonwo came into his life, it's not that his condition got better, it just so happens Woonwo soothes his need of control and his thirst of affection, being someone's sole attention, which also why he's short tempered when Woonwo didn't do as he say.
Woonwo on the other hand, the kid who's too used to give up, his life a series of misfortunes and he believes the harder he hold on to something, he'll lose it. He's too used to abuse that he came to think it's faster to take it than fight against it, and give up rather than fight for it, after all nothing goes well with his life. Much the same with how Seo-an turned a control freak (which ironically exacerbate his anxiety) as a coping mechanism, Woonwo turned pessimistic as a coping mechanism (no disappointment if there's no expectation). But he sees Seo-an and he realized that things he did wasn't for vain, which led him to become more positive and open to try new things he otherwise wouldn't before it.
But traumas isn't that simple. Seen in how Seo-an still can't stand up against his father and the expectation placed on him, and how Woonwo couldn't dismiss his father despite knowing that old bastard wouldn't change. This is where, the notion of "family love" takes core, in the most twisted yet basic way. Deep down in their hearts, against the better good for themselves, they still crave to have a place.
They're both exhausted, much too used on being abused, their coping mechanism took different approach, yet they're not so different. Their thought process can't be more opposite and here is where the conflict grew, like two people in a maze searching for the same goal yet chooses different twist and turns.
It takes time to learn other's perspectives, much like the characters in the story and the readers, both Seo-an and Woonwo have yet find the meeting point of their differences.