Responses

The boy Yeongwoon grabs, Gyujin ( I think was his name) isn’t Seo-in’s and Jaewon’s cousin, he’s just Jaewon’s friend and a bully. Their cousin (who’s Hae-yool’s sponsor) is a bit older than them (around Taegu’s age so early 30s whilst protags are 26), he’s shown in one of the flashbacks pinning Seo-in down whilst Jaewon tears up Seo-in’s drawing.
So the cousin had this inferiority complex against Seo-in since childhood. Projecting his insecurities onto Seo-in by bringing up his adoption to make him feel better. I’m so glad Yeongwoon knocked some sense into him. An understandable crash out