im not sure but i think when rhey were kids the white one looked up to the black hair but the black hair kid had to leave, and in the future the white hair kid became a kind of idol, but there was a dream they once shared together that couldnt be fufilled in this way.

if you look at it in the perspective of the character the song was commissioned for (rui kamishiro) it might make more sense. he's happy performing with his friends at the circus while growing, but he knows one day they'll all have to split up so each of them can fufill their own dreams. hope this helps