Constanze had already moved on from him, she'd let her heart free and it hurt to see. In some ways he wasn't just like other immortals, as a once living and breathing man of history, someone who he didn't think was meant to be here again, he'd been given another chance. He'd had the door opened again to enjoy the thing he loved so much. Life and his work---and Euterpe had brought him a new vision. This wasn't easy.
His breath shuttered and he felt his heart sink. "You shouldn't have to be second," he said very shakily. "She's moved on from me, I know I have to do the same." Just for Mozart it was as if she'd died and he was the one living on without her. This must have been what she felt when he left the world so young.