I like this story very much. It's a clever way of bringing Snape back to life, one I haven't seen before, with enough detail to make it convincing but not so much hand-waving that the question of 'huh, would that really work?' overshadows the more important elements of the story.
I love the idea of Harry obsessively reviewing Snape's memories for 20 years, just because it's so very in character for him. He really is a person who tends to fixate on things, or on people, probably because he had so little in the way of real attachments as a child. And also, in Snape's case, I think because Harry is also a person who desperately wants to do what is *right*, and he realizes that in Snape's case, he didn't have the chance.
The interaction between the two of them in the pensieve is lovely, a nice balance of snark and dawning admiration on Snape's part, and of understanding and curiosity and growing desire on Harry's, and I was *so* pleased when they found the last memory and Harry basically forced Snape to acknowledge the fact that he (Harry) does in fact desire him. And the scene where they actually bring Snape back to life was very powerful.
I enjoyed your characterization of Ginny, and was glad that she and Harry had a happy life together, because honestly, the idea of him suffering for 20 years with some kind of self-absorbed harpy is just too miserable, and also IMHO, contradictory to what we know about Ginny in canon; she's young, yes, and perhaps rather shallow in some ways, but she's not a raving bitch. You presented them convincingly as a long-married couple, comfortable together, supportive of each other, accepting of each other's quirks and flaws. Eileen, too, was well-drawn as a survivor doing her best for her only child.