There's nothing WRONG with it, but I don't like it for some reason. Don't take it personally.

Heart-breaking. I can't help but think that it's partially Sirius's fault for doubting Remus. They would have had his extra help and those few extra special moments to help James and Lily.
Anyway, I'm off to go cry now. :P

Good job describing how the distrust in wartime happened, and how even when it shouldn't have been personal, it was.
Very emotionally compelling.

A very good, well thought out piece of work. You describe with tragic inevitability the disintegration of Sirius and Remus’s relationship, the growing detachment and Remus’s incomprehension (he does not suspect Sirius, and he does not yet know that Sirius suspects him). I like your idea of giving Remus the job of decoding intercepted messages; that’s something he’d be good at and would like doing. The scene where Remus finally understands that Sirius doesn’t trust him is heartbreaking; Remus took Snape’s suspicions in his stride, but this is Sirius….
The action at Godric’s Hollow is excellently done; I know how hard these are to write. Of course it deviates from canon in that Voldemort has brought some Death Eaters along, but it’s AU so that doesn’t matter and it makes for a more dramatic battle scene anyway. The ending is not wholly dark, more bittersweet. Sirius and Remus are grieving, but at least they have each other, and Dumbledore knows Sirius is innocent and can prove it. They don’t know how much worse things could be, but we do.
One small thing puzzled me: when Remus went in search of Dumbledore, he went to Grimmauld Place and found Snape there. So, in your AU, the elder Blacks were already dead before the Potters, and Sirius had given the house to the Order? But didn’t live there himself? I wonder if just a sentence of explanation might have been helpful there. Perhaps it would hold up the action too much.
Anyway, great story, a good idea well carried out.

Really excellent. Sharp writing, good characterizations and interesting ideas.