Being Padfoot saved him. Saved him from Azkaban, from madness and death, preserved some of his precious memories from obliteration. But being Padfoot meantbeing a dog, and a dog's memories and thoughts were not those of a human. A human could close his eyes and see James, see his smile and his hair and his glasses sliding down his nose, and the Dementors loved it. They'd rip those visions from him again and again and again, and feast on his misery till he lay on his cot screaming his throat raw.
But emotions were different for a dog. When he'd first escaped, and being Padfoot was all he'd known, he could feel hunger and thirst and exhaustion and pain and fear. But not hate. Hate required a depth of feeling that Padfoot could not fathom. Even with Snape, it was more a simulacrum of hate, because he remembered that when he was human he had hated Snape. And rage, rage was too easy. He'd only have to think of Peter, and his hackles rose, his whole body would shake with an anger that threatened to make his eyes bleed, and the smell and feel and taste of the rat blotted out every other thought or feeling.
He knew pleasure as well, and a kind of happiness that came with a dry place to sleep and a decent meal. And loyalty, an instant and indestructible loyalty to Harry. But even as hate was beyond him at first, so was love. Loyalty was simple. Harry was James' son, and for that alone, Sirius would be true to him to death and beyond, but love more complicated. For a dog, love required trust and kindness and nearness. Any mutt could be faithful, even to a violent owner, but love bound you forever to a packmate, and it did not come easy.
The longer Sirius spent in human form, the more vivid his emotions became. He felt sometimes as if 12 years worth of love and hate and desire and loathing were compressed within him and would periodically burst forth in torrents of rage against Peter or Snape or Dumbledore; or manifest in frantic, fierce devotion to Harry, burning with a wonderful and terrifying fire that flickered at his soul but did not consume him. The emotions were nascent within him, primitive, but real. But the memories were corrupt and unbalanced.
As a dog, the Dementors could find no purchase in his mind, but neither could his visions of James. Sight, even sight-memory, was black and white and dull grey, flat and lifeless. Dog-Sirius experienced his world through sound and touch and taste and especially through scent.
Scent was almost his undoing. During the Triwizard Tournament, when he'd been living as an animal in a cave above Hogsmeade, the acrid scent of a wood fire came curling up the mountainside early one morning and whisked him away to a bonfire he'd had with James on the beach the year they'd turned 19. Sirius could feel the chill of the early summer night and the heat of the fire, could hear the sparks rising upward in an endless spiral, feel James in his arms and smell the blessed scents of smoke in his lover's hair blending with the sea salt. But he couldn't seeJames. He'd slammed his head into the stone of the cave walls again and again, welcoming the pain which neither obliterated nor restored his stolen memory.
And one morning in Grimmauld Place, Harry came down the stairs, and before Sirius could stop himself, he caught the musky, salty smell of semen, and realised Harry had been wanking, and the scent was James. He'd had to leave the room, fleeing to the farthest corner of the house where he'd crouched under Buckbeak's gimlet eye, digging into his arms with his fingernails till blood flowed red down his arm to try to blot out the urge to take Harry into his arms and kiss him as a godfather should never kiss his 15 year old godson.
Remus helped. Remus was the bridge between Sirius the handsome, arrogant Auror and Sirius the crazed convict. He'd made his peace with Remus during those long weeks after Voldemort's resurrection as he'd wakened night after night from heart-pounding nightmares to find Remus beside him, tired face gazing down reassuringly into his, hands stroking his back, anchoring him to his human body when every nerve and impulse screamed at him to transform, to hide within Padfoot.
And when Remus' stroking hands wandered away from his back to give solace and release to the rest of his body, Sirius had wanted to protest, but could not. He needed it, needed Remus' hands and mouth and prick to ground him to this new life, this life without James, without the spur of vengeance that had goaded him on throughout his first year free.
Remus' presence could sometimes still the paranoid, paralysing fear that he would fail yet again and something would happen to Harry and all that remained of James Potter would pass forever into the mist and vanish. Remus was the only one who had never lied, never let anyone down or made a promise that he did not keep. Despite his frail exterior, he was the strongest of them all, and Sirius-the-dog and Sirius-the-man both trusted the kindly werewolf who had waited so patiently for Sirius to be his and never asked for promises or assurances that Sirius was no longer capable of giving
So Remus helped, and time. The healing days at Remus' cottage had begun the process of teaching him to be human again, but all too soon came the move to Grimmauld Place and Sirius realised he was back in prison.
And so here he is. Trapped in a hated house that's as much a prison as Azkaban, in a body he no longer recognizes with feelings that are almost beyond his control as they never were before. The bolthole that was Padfoot is closed to him – he can't hide when everybody is watching him. His Dementors have names now: Albus, Molly, Kreacher. And Harry.
For Harry is both blessing and curse. Sirius lives for Harry, but he doesn't know how to be what Harry needs. Harry needs James. And so does he. But James is lost because Sirius failed and now Sirius is failing again and is losing Harry to despair and confusion as he hides in his room whilst the Weasleys whisper in corners about his vision and how he saved Arthur. And Harry has to go back to Hogwarts to face whatever demons haunt him there alone, and Sirius can't take his place or save him from the pain that's coming.
So one morning when Harry ventures from his room before the house is awake, he surprises Sirius sitting at the kitchen table, staring listlessly into a mug of tepid tea and because Harry is tired, he asks about James. And because Sirius is guilty and exhausted, he begins to talk.
He talks about James the Quidditch star, the youngest player on the Gryffindor team till Harry came along, and as he's telling Harry about James' spectacular moves and how fast he was on his broom, he's remembering James coming off the pitch, stinking of sweat and new grass from where he'd rolled off his broom. A glimpse of the red and gold of James' robe as he spins on his broom flashes like a sunrise. And for the first time, Padfoot's memories shatter and Sirius sees colour in his mind's eye.
He talks about James the prankster, leading them from the dorms to the kitchens in dark of night under cover of the invisibility cloak, and Harry smiles with James' mouth, and in watching Harry, Sirius sees James, really sees his smile as he cajoles the house elves into giving up yet another plate of cakes. Nobody said no to James Potter. The vision lasts but a few precious seconds, but it is in his mind for the first time since the Dementors ripped away his past like raptor birds pulling the flesh from their prey.
He talks of James the Auror, fighting Dark Wizards at Sirius' side, leading their men with skill and humour. And he can see James in his bronze leather jacket, so handsome and strong, he can feel James' silky hair under his hands, and taste his sweet breath as he kisses him. He tells about late night patrols when James would come back to his London flat and they'd stay up late, talking, laughing, drinking. He doesn't tell the rest, how those late nights would end in Sirius' bed, James glorious body spread under him as he slid between those long legs in slow, deep strokes. But something in the look in Harry's eyes makes him think that maybe Harry knows anyway.
And then, because Harry needs to know his mother as well, he tells of James with Lily. The joy in James' eyes when he rushed into Sirius' flat, she said yes, Padfoot, she said yes! And the bachelor party, where Hagrid had made James drink from his tankard and refilled it constantly so that the groom-to-be was retching into the sidecar of the best man's motorcycle, and Sirius had tucked him chastely into his own bed and spent the night on the sofa. Of Lily, so beautiful in her wedding gown so that even Sirius who had little appreciation of feminine pulchritude was struck dumb when he saw her standing at the door of the little church.
And so he brings James to life for Harry, and in doing so, sees James' face, hears his voice suddenly crystal clear after 15 years of seeing and listening through the perverted filter of a Dementor's maw. As he tells Harry of his father, Sirius is finally able to remember James in the way that humans do, with details as sharp as knives that cut into his flesh, and the words flow from him in lieu of tears he can never shed, for dogs don't cry.