
My interpretation is that jae-kyung killed himself and that happy moments was him imagining a different and happy life for himself the one he wanted and rightfully deserve
I don't blame anyone except the parents for jae-kyung his friends were just teenagers themselves they did as much as they could

just to add onto this, I feel like once he went back to his father the cycle just continued—and that was where the delusion of happiness started. he cut off kwon and hansol and kept them cut off until he was pushed to a point of no return. he killed himself in the end, and the rush of scenes in the last chapter were what happened in reality as jaekyungs mental state kept deteriorating further snd further. ultimately he dreamed of having a good relationship with his father, and a friendship with kwon and haesol. it’s unfortunate that it would forever stay a dream.
Finally! That bitch is gonna get karma for killing heeso mom I'm so happy