The actual thing that makes Autumn not really work is that the main love interest, Nerine, is only barely a character. She does have a personality and things that she struggles with, but anything besides "nice girl" is introduced basically in the second to last chapter. Nerine struggles greatly with the contradiction between her faith and her love for Yuzuriha, compounded by guilt over how badly she's treated Yuzuriha in the past, and that should make something at least passable. But she doesn't really get room to express anything because so much of the runtime of Autumn is the two of them pretending nothing is wrong or just not on speaking terms, and that always comes at the expense of Nerine's development, because she's not the POV character.
Yuzuriha is left over as a lesbian who's spent her whole life pining after a girl who's she's built her entire sense of self around, who will (as far as anyone can tell) never return her affections. In my opinion, Nerine is too out of focus to sell a story where the two of them reach some semblance of understanding with each other. Because of that, I think it would have made more sense to tell a story where Yuzuriha finally moves on, which can kind of happen. There is an ending where she dates someone else, but not one that tackles the subject of Yuzuriha getting over Nerine or figuring out who she is if not a vessel for what Nerine wants. The story has a conclusion it wants to get to, but it wrote an outline worth of material for Nerine and didn't bother to write anything more, and you can't make this story work on that.