This is exceptionally thorough in detail and elucidates Sam's character really beautiful. It's an AU that doesn't at all feel AU-ish, if that makes sense, and I think that's a credit to your workmanship, which is exacting and precise. The development of Sam's character, and Dean's very in-character response, is nicely emphasized by the one constant always true of these two: that they love each other.

Bravo!