Translator here! Unfortunately, the reason isn't mentioned, but from what I understood while translating this manga, Hiroya just fell out of love with him. Him saying that he wants to be his junior again was more like him saying that he wishes he could love him like he used to, but just isn't able to anymore.
Hello translator~~ hope u have a great day. Ohhh soo i was kinda have a slight that must be the reason also fell out of love cause way b4 i read this update. I saw some topics in X about those long time relationship saying they still love each other but still deciding to break up when the only reason others do it cause they fell out love... Ugggh love is scary and complicated
I cant imagine having someone in your life in the past (u had sex with them and everything) then seeing again like ahh... Im dumb but did it mention the reason why they broke up i mean Hiroya says he wants to be his junior again(?).. what's the meaning of it!??