Wonderful ending, I was genuinely moved.
What Kazehaya said at the very end really got to me. It wasn't anything revolutionary, in fact it was sort of cliched, but none of that matters when put in the context of this series and what the characters have been through to get to this point.
"[Being a girlfriend] is not a job; just be yourself."
I imagine that was exactly what Kuronuma needed to hear. Hopefully she takes it to heart.