You have to listen to the song by The Oh Hellos "Hello My Old Heart". I don't know how the author found it, but it is the perfect song for this story. But, don't listen to the song until you've gotten to that part of the book. It just won't be as meaningful if you listen before you read that far into the book. (It was page 207 in my copy)

Here it is on YouTube: https://www.youtube.com/watch?v=AObC5VKMdEc