well it was ended that way for the sake of plot only. It was totaly out of character for her to leave that way. All through the story, she was the one that had no problem with the relationship at all. She was super obsessed with sora too, and ...

I've read doujins like that, I've also read the opposite. You got to take into account they draw 17+ pages a week with only a few assistances while doujins are drawn in months and months with only 17-30+ pages.