Whats with all the"murder" stuff?

police dude basically adopted the child and after he grew up they became lovers, but silver hair kid thought the police dude wont like him enough and move on in retirement, so he became a phyco murderer so police dude cant quit

The police man found the guy when he was a kid, because he was being abused by his father (a mass murderer, that seems to have killed the mother). So the police man took care of him. The silver hair guy believes he must become a killer so he can always be "chaised" by his hyung. In his twisted logic, he believes becoming a criminal is the only way for them to be together, earning his hyungs attention (even tho the police man obviously doesnt know he is the killer, but for sure he will at some point). Its nonsense for someone like us, but he is sick so.