Just watched WHC 1 - Beomseok character was beautifully written
As someone who has had similar childhood I absolutely love how the character was written in depth.
He is not black and white but has a fully gray side.
Why I think he behaves like this is most of his childhood he was abused and hated at school and behind closed doors.
When he met the group he saw Sun ho has a ray of light similar to how Si-eun did. Except he became scared to lose it and in that anger he takes series of bad decisions.