Responses
Right?? Like what do we know what conclusions Byul reached regarding the situation between His mom and Grandma when no one explained things to him.. all he must have come up with was that Hyesung was abandoned PERIOD and He knew he was almost abandoned but Hyesung decided to stay and love him endlessly who could say that Byul wasn’t naively thinking that “If my mom changed and loved me after thinking of abandoning me, Grandma must have also thought the same”

I feel for Hyesung, but Byul's reaction is realistic. Byul only knows that her grandmother abandoned her son but not the abuse and others details, and no one explained his childhood to him in detail.
Let's be clear, no parent tells their children too many details and traumas from their own childhood, and teenagers develop their own traumas and reasons for rebellion.