I interpret this as reflecting on a relationship, that even though it may have ended (the fact that the tempo changes seems to indicate something happened) but the person still serves as a muse, hence the "Is it any wonder why I write... pages layered upon pages".
I interpret this as reflecting on a relationship, that even though it may have ended (the fact that the tempo changes seems to indicate something happened) but the person still serves as a muse, hence the "Is it any wonder why I write... pages layered upon pages".