Responses
Gren has to save himself. No one can do that for him. Sadly, drug addiction is awful like that. Gren wants to pull Shin down with him. Chasing Gren away was hard for Shin, but it's necessary in order to save 3 lives (Gren's, Jake's, and his own). Also, both Jake and Shin's friend Hosung (who both saw Gren's criminal records) warned Shin that Gren is not the same kid he remembers from his past
Maybe because I have a younger brother that I feel so sad seeing Shin chased Grens away. Though he did give Grens some money to somehow survive the street life. But with his addict problem and his wounded foot, it'll be hard for him to move forward in his life. And by the look of it, Grens still hanging on loose hope on Shin. I thought by having the same childhood trouble they will always had each other back, I guess blood is still thicker than water...
I feel so sad with Grens that I couldn't even enjoyed the subtle development on Shin and Jake's relationship