Responses

jae-bom is the hyung/sunbae from his old school. he appeared in the first chapters as joo-young's ex (the famous singer)
ykno joo-young transferred to new school and meet jong-han rite. they got along but later drifted apart, mostly because jae-bom approached joo-young in his final days in high school. then joo-young went vanish without news, he cut contact with jong-han and didn't tell anybody about his whereabouts
memory so bad its only been 3 months but i forgot why they drifted apart