Oh, this is so unfortunate.  One wonders how he could stand doing what he had to do when so many things went pear-shaped on him.  I kept hoping through it that you would invent some way to go AU and save her at the end. 

I feel so sorry for him. Every one he gets close to is destroyed by this demon. It's a wonder he hasn't lost his will to live completely. Of course he is strong but that doesn't diminish his pain.

Oh, this was so sad, knowing what was to come. I could just hear her calling his name before her death. 

How sad!  You've very nicely shown just why, in canon,  he never let himself get close to anyone after Lily's death.  I have no doubt he will make sure Em's death was not in vain.

Awww. That's so sad! Beautifully written, as always, though.