This ending left me a void, and it's not a void of future nostalgia, in my opinion all three protagonists have a very sad ending:
Jindou is dead, and it will be as if she never existed.
Ayumi has lived and will live in ignorance of everything the fuck happened.
Kouki knows everything but can't talk about it, why? He cannot even cry his friend to whom he is so indebted.
We could say that it is a courageous ending, the author did not try to please the public like others who try to please everyone with alternative endings and screwing up the course of the whole story.
It's a risk, many will not like it, like me, but it's a choice and I prefer that the author has free choice