Just want to welcome all the new Hanabro's to the board. She really is wonderful isn't she?
I definately agree that the bad endings are heartbreaking. Hanako and Lilly's probably being the worst. At least IMO. That being said, I think Hanako's is worth experiencing at least once. I'd suggest checking it out on Youtube. So it doesn't feel quite so personal.
As for fanfic, Sisterhood is considered by most to be the real continuation of her story and is a damn good read. If you think you love her now, just wait.
http://ks.renai.us/viewtopic.php?f=52&t=6750
In the end, the feels will lessen with time. Or at least be less painful. It helps to hang out here with us to talk about it. Search Google and Youtube for a ton of KS related content, and browse fanart and read fanfic. Maybe even create some yourself. Those things are really the best cure.
In the end, I think this pic pretty much sums up how most of us feel.