Remus had always known more things about the world than Sirius. Ever since they were boys, real, honest-to-goodness boys who slid down Hogwarts banisters and took their broom flying lessons and ran about with grass stains on the knees of their trousers, Remus had known about things Sirius had no earthly knowledge of, nor could he imagine them.
He knew about the breaking and splintering and changing of bones, and the healing of them. He knew what it meant when James didn't eat his potatoes at dinner, and what it meant when Peter offered Sirius a chocolate frog. He knew to follow after Sirius' temper, not to run from it; he knew how to coax Lily into sitting with them in the library, even (and especially) when James was being as great a berk as he could manage, which was actually quite often.
Remus knew that Sirius loved him, whether Sirius said so or not.
Later, he knew how Sirius took his coffee. He knew to leave the bathroom door open so that when Sirius woke they could shower together; he knew what joke Sirius would tell over supper. He knew when to avoid Dumbledore's gaze at Order meetings, and he knew how to make Harry laugh. He knew what it meant when Sirius forgot to kiss him good-bye.
There were two things that Remus didn't know. One, that Peter was the traitor. Two, that Sirius was innocent.
Those turned out to be the most important things he had ever needed to know.
Instead, he knew what it was like to suddenly have no one who knew you. He knew what Muggles taught their children in literature during forms one, two, and three, because he was the one who taught it to them. He knew how to make tea with an electric kettle. He knew the chill of a too large bed. He knew how to sew a patch on a cloak, and he knew that the itchy place inside of his chest, just behind his breast bone, would never really go away.
Remus knew he'd never be whole again.
Finally, he knew the truth. A world of difference, Dumbledore had told Harry, and Remus knew that was true. He knew when Sirius would run, and when he would appear at Remus' door, as Padfoot. He knew Sirius no longer liked touch, or too much light, or the way his knife scraped across a plate as he was cutting meat apart. He knew when to read The Daily Prophet, and when not to. He knew Sirius shivered when Remus walked the pads of his fingers into Sirius' palm, but that it was the good kind of shiver. He knew what it meant when Sirius sat next to Remus at supper; he knew how he looked at Sirius when he thought no one was looking, and how Sirius looked at him when everyone was looking. He knew Sirius thought himself unlovable, and incapable of love. Sirius thought fear conquered everything, even love.
Remus knew better.
He knew Grimmauld Place was a haunted, moaning, disgusting, dusty trap of a dwelling, but he also knew that it was safe. He knew how to light the fire in the kitchen; he knew how to walk past Mrs. Black's portrait without waking it. He knew not to trust Kreacher. He knew to trust Molly. He knew Harry needed to be handled with care; he knew Ron and Hermione were up to the job, even if they did not. He knew when he could leave the house and when he needed to stay. He knew Sirius felt the fractures in his heart would never heal, but Remus had always known more about broken bones, and hearts, than Sirius.
Today, Remus knew he would find Sirius in the library. He knew Sirius would be toward the back, in the window seat that looked out on the busy street at the front of the house. He knew Sirius wouldn't be reading, but would be watching the people coming and going, hats pulled over ears and scarves blowing in the wind. He knew there would be the occasional umbrella, as the sky was a dark grey, threatening pedestrians with rain. He knew Sirius would start when Remus sat down next to him, but then give Remus a smile. He knew it was a small smile, but that it was a real one. He knew they would sit together in companionable silence, until Remus broke it.
Remus knew he would.
"I know about more things than you do, Sirius," Remus said.
Sirius looked away from the window, and over to Remus' face. His eyes were the color of the sky outside. "Always did, Remus," Sirius replied, another ghost of a smile passing across his lips.
"I know I should have trusted you before, like the way I do now."
No smile this time, just a flash like lightning in Sirius' eyes. "I could say the same."
"I know that, too."
This time, the clouds in Sirius' eyes began to part. "Of course you do."
"Know what else I know?" Remus asked softly, his heart skipping a beat.
No joke, no flip remark, just soft sarcasm, and a little trembling vibrato underneath Sirius' voice. "I'd ask, but I'm sure you're about to tell me."
"I know that love isn't meant for the young, or for the strong. It's made to make pieces whole, to fit parts together. Everyone who has ever really loved has known loss of some sort. Love is meant for mending."
Sirius lowered his eyes. "There are some things love can't mend, Remus."
Remus took Sirius' face in both hands, and lifted his head, palms warm against the slight stubble on Sirius' cheeks. "No, Sirius. Love is the passion meant to bind and fuse and make whole what is not. Let the young have infatuation; let the unscarred have romance; let the innocent have wine and roses. But let us have love."
"How do you know this is true?" Sirius asked.
"Because I know that I love you, and I know what that means." Remus traced his thumb across Sirius' cheek.
"Hmmm," Sirius hummed. "That's one thing I know, too."
As Remus leaned across the gap to kiss Sirius, he knew Sirius' lips would be warm, and that the heavens had opened outside and the sky was pouring down rain. He knew he didn't care what went on outside, as long as he could continue to kiss Sirius and feel his warm weight in his arms.
Rain splattered against the glass, but no one inside knew it.