I just got back to reading manwhas and mangas again after years, I remember reading this story about old friends, one is I believe a blonde and the other one has a long black hair and wears glasses.
Black hair guy left, making the blonde mad. Years later they met again but the black hair dude now works for blonde and they have a rough relationship, black haired guy is secretly a singer too and gets along with the blonde with the singer persona
That's all I can remember, I've been looking for the title of this story for months now :'))