Wow, extremely inventive premise! This read like a gothic fairy tale. Not to spoil anyone, but I was sure that the ending would be different. But the one you've chosen fits well and leaves the reader open to assign their own outcome (mine is happy, of course, as we have Harry's sharing of Severus' path). Great use of the secondary characters--this trio is how I picture them and Severus' moments of realization and appreciation of them are lovely. The last sections after Severus' encounter with the owl are beautifully done--the reader really has a clear picture of what his world has become, and how his view of it is changing. Just heart-breaking, yet a bit hopeful this story.
I can't believe how well the art complements the story. The dreamlike, fairy tale quality, the attention to "world-making" are incredible. And the scenes you've chosen to include were very well-selected.