Apologies for the lateness of this response - life has been a bit overwhelming. But thank you for noticing and appreciating the various strands of the plot. I had a kind of temporal parallel set up in my mind: Lily as the past, the compelling reason for acts of further sacrifice; Harry as the future, the golden Gryffindor, eternally hopeful; and Snape as the dubious present, on whom everything hinged - both the meaning of the past and the direction of the future. Past and present had to reconcile to make the future possible; or rather, the past had to give way to the present. Put like this, it's much too schematic and not really what I intended. But something along these lines hovered at the back of my mind while I traced the emotional triangle of Lily, Harry, and Severus that provides the story's structure and its heartbeat.
I'm so pleased you liked Lily! I had no idea when I started writing what kind of person would emerge. The hints in canon certainly don't persuade me that she was saintly while alive, in fact she was fairly testy with Severus, at least in his memories. Her choices seem those of a typical teenage girl who'd grown up attractive and assured, neither especially tolerant nor introspective. Yet she did bond with Snape as a child; they must have shared more than magic. And in truth, he was hers, even after she dropped him. When he finally makes peace with the past for Harry's sake, she knows enough not to hold him back. Because it would, in the most literal sense, have killed him. So she lets him go, only this time for far better reasons.
Thank you again for reading this and for letting me know what you thought of it. :)