Wow. That was really nice. Very touching. Great description!
Well, first of all, I really liked your story. I really love your style, it's both distanced from Harry and giving insight in what he really feels without needing a lot of words. I think you did a good description of how he could feel after Dumbledore's death and, most importantly, it sounds realistic. You show Harry as a vulnerable human and I'm very thankful for that.
By the way, isn't "Dies ira" a sequence of the"Totentanz"? I remember it being something about the Last Judgment. "Dies ira, dies illa, finet saeclum in savilla" or something like this, I might be mistaken with the "finet". Where did you get the idea for the title? It would really interest me!
Oh, and I'm from Germany, too and quite familiar to the "foreing flaws", too :-)