The return to earth, the right place for love (as Frost will say). One fall or two: that's another way of asking the question of how to think of God.  Calliope can't defend Orpheus because she is an empty dream.  Orpheus's turn to Eurydice as a turn to the fact of mortality: all mortals are empty dreams. Fall of Eve, and of Adam: "And me with thee hath ruined" = first silent thought.