Takes place after the scene with Arthur in the hospital, but before his friends 'intervention'
For Starrya47 who requested a Sirius and Harry moment. Any more requests, have at it.
Harry tried, he really did, to keep himself to himself during his stay at Grimmauld place during the rest of his winter stay. One person in particular wouldn't have it. Sirius came up to his room, let himself in, and then closed the door behind himself before Harry could protest.
"So," Sirius began, digging his hands into his pockets and casting a look around the grim room, "how was Arthur?"
"Good," Harry said, eyeing him curiously, still trying to figure out why he was in here.
Sirius waltzed over and sat down on the edge of the bed, now eyeing Harry curiously as he continued, "then what's bothering you?"
Harry couldn't tell him, he couldn't tell anyone, so he swiftly changed to something he'd been wanting to ask his Godfather, "what's your Patronus?"
Sirius released a surprised snort of laughter. He could tell Harry was diverting, but he gave him the benefit of the doubt, and a swift smile appeared on his face as he answered. "A dog, of course. Made me laugh like crazy when Remus told me what your's was."
The conversation spiraled out from there, and for quite some time Harry and Sirius just sat there and talked. Only a light conversation, inconsequential in the scheme of things really, but it was a small treasured moment to the both them.
Sorry it's so short, but I tried my best to fill in a moment that I fully agree was missing from the books.