He's not stupid; he knows what James and Lily and Remus whisper behind his back.
"he's not himself.
he's depressed.
he's broken."
They're right. Marlene was his everything, and in less than a day, she was gone.
So what if he didn't laugh and lived harder, always rebellious, without her?
She made him want to get up in the morning. She made him want to smile, to laugh, to prove his godforsaken family wrong. She made him want to live.
And now she's gone, cold and wrong.
She was so still as they lowered her into the ground—
She was life, constant motion, laughter and love, to see her motionless was jarring and so so so wrong.
He threw himself into every battle to get away from their, his, the apartment, where her scent still lingered in the sheets he can't bring himself to wash.
And then. See, he'd known Lily was pregnant, that she and James were going to have a kid, but he'd distanced himself from them after Marlene.
So when Remus came tearing into his the apartment, yelling about babies and St. Mungo's and "where is the damn floo powder, Padfoot, Lily is giving birth we need to get there right now," he'd blanked.
He went to St. Mungo's, and then the next thing he knows, little Prongslet is being placed in his arms, James smiling so widely his face should've cracked and Lily is laying down in the bed, tired but smiling too. He hears them say something, but his whole focus is on the baby in his arms. Finally, James shoots him with a stinging hex to get his attention and says "we'd like you to be godfather."
And in that moment, his worldview adjusts. The most important person in his life is that little boy. His godson. Harry.
Thirteen years later, he breaks out of Azkaban with a broken heart because Marlene is gone, he's spent thirteen years being reminded of that, but also determined to get to Hogwarts because Harry needs him. Harry has no idea the danger he's in with that rat near him.
When he sees Harry after thirteen years, he's awestruck; there's James and Lily's boy; his godson. Thirteen years old and ready to attack a supposedly dangerous man to protect his friends, and hours later, help him escape despite knowing the truth for a few hours.
And then, two years later, he's reunited with Marlene, with James and Lily and everyone else the war had taken from him, and he's finally at peace when Harry joins them a hundred years later.
