They're both so awful at communicating that they're at different planes of understanding what they are to each other. To Sae it's like throwing a child into the pool to watch it learn how to swim from a safe distance, but the child--Rin doesn't know why he was thrown away
i enjoy the optimistic tone of the omake. it feels like sae is just waiting for rin to have the kind of metamorphosis hes envisioning. it assumes the underlying ego is there, but it needs to be seized and tapped into