I think the hair decorations are different between reality and "Beniko and Sora" (Empty vs Filled, Scrunchie vs String?). Rereading it that way, it looks like the real Saku never left her notes for Kasumi to see. There are some tricky transitions in there!
Ding ding, we have a winner.
Man this oneshot is awesome. I figured after the ending that most of it was the in-story story, but this extra layer makes it even better. Check out page 14 to 15, her hair decoration changes between pages: 14 is real (or at least, until the desk slam) and then it stays with the string until page 27. What a great detail.
So it's sad to see people missing the point calling it "cliche" and "disappointing". Wouldn't it be cliche if it really was a requited love and they both lived happily ever after? :p