I honestly don't mind the bad end route that the story took; not all stories needs a redemption arc.
Sure, the ending is abrupt, but whatever feelings that Clauden had before towards Luan has now been completely shattered and turned to dust.
For what I can see, their relationship seems beyond fixing.
Also, I'm sort of glad the author stood by their choice and clarified that the upcoming side stories are entirely optional.
That said, I do hope they create another route where Clauden finds new happiness, far away from Luan/ML.