sooyeon isn't the legitimate child. he's a child of gisaeng (concubine)
the reason why beom is always bullying sooyeon because he fell in love with him. but they're half-siblings, so it's impossible to be tangled in romantic relationship. that's why he's crude and treating sooyeon like garbage. because in beom's perspective, if they can't be lovers, then it's better to be someone who will stay forever in sooyeon's mind. and what's the easiest way to being memorized by someone? giving them painful memories of you ofc. because humans are naturally harder to forget people who hurt them
Ooohhh now thats make senses ╮(￣▽￣)╭
Im still wondering why beom chose to bully seoyoon if he loved him so much, is it bc of jealousy too that seoyoon is the legitmate child?.. is he that insecure, thinking that seoyoon would never love so he chose to make seoyoon resent him and even willing to be killed so seoyoon could remember him for the rest of his life （￣へ￣）i mean like u could choose a better way but now hes regret it
┑(￣Д ￣)┍ pathetic i may say