Yapping Part 15

Chapter 65: I mentioned before that Sangwoo was so consumed in his delusions and failed to escape from his mother, thus continuing to see her in Bum. Sangwoo's “I don't need you anymore” showed that he didn't see Bum as a substitute for his mother when Bum failed to kill Seungbae because had it been his mother in Bum's place, she'd have killed Seungbae. In Sangwoo's psychotic state, he couldn't see other connections that tied Bum to him anymore once he stopped associating his mother to Bum, which explained why he had the drive to kill Bum.

Chapter 66: The panel where Sangwoo let the picture go was probably him letting go of a part of Bum which was different to his mother. If we go back to Chapter 37 at the amusement park, Sangwoo had a lot of either confused or shocked expressions. While his mother was always depressed and zoned out outside of the house, Bum was the complete opposite of her. Chapter 37 is where he got to see a lot of Bum's sides that contrasted to his mother, and Bum's bright face on the rollercoaster must be the last push that urged him to let that carefree part of Bum go. Bum's innocence was unfamiliar and not necessary, since what he needed at the time was a substitute of his mother, hence the act of releasing the picture was him releasing that part of Bum free.