Oh, thank you for such a marvelous comment! I love the term Severusness, because yes. I have certain highly developed opinions about that quality, and it's partly what drives me to write fic. ;)
When I started this, I had to sit for a while just contemplating the world from Lily's POV. Because as shallow as I found her in canon, there's one huge inarguable debt hanging between her and Severus: the fact that his terrible mistakes led to her death. So unless I wanted to approach the afterlife as a place where everybody suddenly understood everything and it was all sweetness and light, the issue of Snape as an inadvertent murderer had to be addressed. Lily had excellent reason to hate him for all eternity, and the trick was in guiding her from that perfectly plausible position to one in which she understood him at last and could even love him again.
Hanon exercises, hah! I figure that Severus would devise an entire repertoire of tactics for getting Harry out of his hair when he just couldn't take it anymore.
As for Albus: let's just say that he orchestrated everything he could possibly orchestrate except for the part where Snape breaks the hold the past has on him, freeing himself by falling in love with Harry. I don't think Dumbledore ever actually intended to give Severus up, but Lily foiled him there.
The locket! *bangs head on desk* I know! Someone else pointed that out to me, but too late! Oh, the shame. I'll fix it before I repost anywhere. That was an instance of me sabotaging myself - I could swear I wrote "locket" in an earlier draft, but then when I decided to include references to Return of the King I re-read parts of the book and then I re-watched the movie, and I'd always rather thought the locket was a rip-off of Tolkien's ring . . . Anyway, apparently my hindbrain decided to slip one over on me, and I didn't even notice. *is mortified*
I'm utterly delighted by your pleasure in my fic, and especially in my version of Severus. Thank you so much for reading!