Ok, now I get it, hot blueberry just has a crush on his little brother and wants to protect him. That's probably why he sabotaged Dojun's first love at school and vehemently tells himself that they are definitely not biological brothers. Which, however, earns Dojun's hatred. It just looks like an unhappy love, and he suffers for it.
So I feel quite sorry for him.
So I feel quite sorry for him.