This was so great! There are so many places that I'd like to comment on that this would almost as long as your story!
I adore how you managed to keep James alive, but still create the Harry that we know from the books, though there is a major difference of not having a dark lord after you, which allows him to grow so much more emotionally. Of course, he still is relatively clueless, being a male, so it was so poignant when he realized how he mis-read Severus' attentions.
Him trying to set things right is just so much love! His standing up to James, being so much more clear about going after what he needs instead of being the good little Gryffindor is also a function of not having to be made into the perfect weapon by Dumbledore--brilliant how you wrote the Dumbledore/Voldemort rivalry. It makes so much more sense than canon that the strongest wizard in the world would take care of the most powerful dark lord in history rather than leaving it on the shoulders of a mere boy.
The dialogue was so wondrously funny, I've been muttering and laughing all evening--it's been driving my husband nuts! The interaction of Harry and Severus was amusing, endearing, and later soooo very hot! The belt and the bonds, ooooh what a blistering image!