Sono Mono. Nochi ni... (NARIIE Shinichirou)

From Titan Manga:
Wazu's life was forever changed when he was rejected by the hero's party and forced to leave his hometown. Once a weak, ordinary boy, he spent two years training alone in the mountains to prove his worth. Now, stronger and determined, Wazu returns to a world that has moved on. Only to find his childhood friend, Aria, engaged to the hero who once mocked him. Heartbroken, Wazu embarks on a new journey, facing misunderstandings, new relationships, and the challenge of finding his place in a world that has changed.