WARNING FOR TRIGGERING STUFF: There is a part that includes a guy with depression who self-mutilates, and it's very explicit. Be warned.
This one is very long, and also one of my favorites. I don't know, you just get attached to the characters, you get to love them, to understand them, and their relationships grow further right in front of your eyes... It's really a good piece of work. You should totally read this one when you got the time. x
Komatta Toki Ni Wa Hoshi Ni Kike!