He was made the scapegoat by his family for them fleeing and leaving him there, when in reality Seungho's father had all of the neighboring families killed and then fled somewhere and abandoned Seungho. That's why the servants talk about him being a monster that the fam
His family never really cared about him maybe. They didn't even shut those people who talk bad about Seungho. Maybe something happened in the past and blamed it all to Seungho
Seungho's behavior now makes sense. And I got a feeling that only NaKyum can change him.