wait so did the younger brother left or not?

He eighter left and went back in the spring or just never left and we see the next morning (after the wedding).

I reread and I'm pretty sure he's never left. The gate is open, he standing in the courtyard, starts walking toward the blossoming tree which is a metaphor of Jeongyeom (bc Dongim renamed him so Jeonyeom means "blossoming plum tree")