So, you almost scared me away with your first line, but I figured 'oh, come on; take a chance', and kept going. And then I was completely hooked in, not only by the story, per se (though it's captivating) but by the language, the lucid flow of your phrasing, the concise vividness of your descriptions. 'Sharply sweet, like a cloved orange left behind long after Christmas has passed'; 'the bottom of her foot, briefly visible, soot-dark with soil. In a clump of grass behind her, her trainers lay in a pile together with Snape's, their laces entangled'--so many lines like these, which are poetic in their compression, in the way they use precisely the details needed to convey the image, and no more.
Harry's need here, his desperate repeated efforts to communicate--both to Lily and to Snape--his love and his gratitude, are so moving, and make me just *ache*, not only for Harry, but for Snape and Lily as well, for their lost youth and their missed chances, and the sacrifices they will be called on to make.
And the ending, for all that it made me cry, is just right. Because I think that the memories *are*, for Harry 'an Erised he cannot resist', and I think he knows that, too, and is brave enough to let them go, so he can go on with his life.