Aww this is so sad! And sweet at the same time <3
I think the concept is wonderful, I was immediately hooked when I understood what I was supposed to do. And this is so beautiful that there are two parts of the story. Life goes on, and there is always beauty in it, expecially when you keep these memories.
I also think the tracing mechanic is a good game design decision. What made me a bit confused is that I think that gameplay is a bit counter-intuitive: I tried so hard to keep the things from dissappearing and after a couple of minutes got tired and thought that this is it and there is nothing more left to do. I was quite surprised to see there is more gameplay, and it happened only because I left the game window open for a while :) It was slightly misleading for me that in order to proceed you have to stop doing the main thing you were asked to do. Or maybe I just wasn't patient enough :)
As I started playing, I thought that I was to trace the objects and each new object would let me see some memories that these two had. It would be really exciting to see more of their together-moments!
A very inspiring entry all in all :)