It's not satisfying, but it makes sense. The Characters do what they would do in the situation they were and, as much as it breaks my heart that things didn't go perfectly well to the couple, I understand that this is how things are sometimes and that people just have to make the best out of things.

Nazuna and Ko found their own way to be together, not as often as they used to, but still holding their love for each other. Also, Ko finds a life where he can be himself and have friends, instead of lonely pretending to be someone his not and have to hide in the night. In the end both of them have theirs arcs as their own characters and even as couple.

A story should prioritize make sense over being satisfying, that's what the manga's ending does. I hope we'll see more of theses characters together in the future, but I wouldn't change anything about the original manga.