the simpliest way to describe it is
that when you finish school, you grow up but at one moment reality hits you hard and you realize that it's much harder to maintain all those good things
also I never expected them to show all those scenes in such mature way
I guess we will probably all be crying tomorrow at ep 16...
but overall after watching ep 15 it already feels like whole happiness in the world just disappeared and there is that void, an empty space... which you can't really fill with any other emotion