what is that book?

[johnkgr]

So I read this book a while back and the story went like this:A girl meets a boy , they fall in love, and she is describing everything that they did together till they broke-up. In the end it turns out that all that was a goodbye letter she wrote and gave to her bf along with a box full items like a ticket from a movie they went to and other things like that. She left the letter and the box outside his door and left. That's all I remember. It would mean a lot to me if you could help me with this.

Thank you for you time.