You make a compelling point. Without Taeju, Euihyun would have likely committed suicide, leaving his younger brother to face the loansharks alone, which could have led to an even worse outcome. Taeju has much to atone for, and his environment is extremely negative. However, despite these challenges, Euihyun is loved. At some level, Euihyun feels this love and is slowly learning to trust. He is beginning to realize that he has someone willing to kill for him, someone he can rely on. Taeju is teaching Euihyun new things every day, just as Euihyun is teaching Taeju. They are a perfect disaster that ultimately ends up saving each other.
Is no one really noticing that no matter what if Taeju doesn't go away or at least makes a 180° change Euihyun will never be happy?? This is his fault and everyone is glorifying him like he isn't just as bad as the others