The Shrieking Shack held a lot of memories for Sirius. There were painful memories of desperately wanting to go inside and soothe Remus as he cried out during his transformation, and not being able to, knowing Remus wouldn't be happy. He never let any of his friends be present for the actual transformation. He was worried that they would see him for what he thought he truly was, a monster. Sirius, though… Sirius could never see Remus as a monster. No matter what Remus thought, he was never, isn't and will never be a true monster.
There were happy memories of secret picnics, stolen firewhiskey and food from the kitchens laid out on a blanket, the four Marauders all laughing at whatever story Sirius or Remus was relating. The Shrieking Shack became not only their hideaway for Remus' transformations, it was also their secret meeting place whenever they wanted to have a party, just the four of them.
There were sad memories of trying to console Remus the day after a particularly difficult transformation, trying to convince him that he wasn't a monster and that Sirius, and the others, would always be there fore him. Just more broken promises, Sirius thought, stretching his tired limbs after transforming into his human form for the first time in months. What he needed now was a place to lie down and a chance to rest.
Remus walked around the house, reminiscing on times past, looking for another room, any room with a bed, but he already knew there wasn't one. He just wasn't sure whether he could take the memories if he stayed the night in Remus' old room. After a while of making sure there was absolutely no chance of finding a bed in any other room, Sirius resigned himself to sleeping in the room that held the most memories.
Sirius walked in, breathing in deep, smiling lightly at the familiar musky smell and a bit of Remus' cologne that seemed to have clung to the pillows all these years. Whether the smell was actually still there, or it was just Sirius' imagination, it didn't matter, because it was there to Sirius. The smell brought back the amazing memories of all the times when he was close enough to Remus to smell the spicy-sweet scent. Those were some of Sirius' favorite memories, and he hoped to be close enough to smell the cologne when it was actually on a person, and not just pillows making him tear up.
Sirius lay down on the bed, groaning at the feeling of the first mattress he'd encountered in over a decade. It wasn't even a particularly comfortable bed, but to Sirius, it was like lying on a cloud.
The room itself was in shambles. There were bite and scratch marks on the furniture and walls. The furniture was dusty and starting to fall apart. But for some reason, Sirius felt like he was back home. For the first time since he left Remus that night, Sirius felt like he belonged. He felt so close to Remus, being in this place again. There were signs of him everywhere- the torn bed sheets, the scratch marks, the smells- and while this wasn't Remus' favorite place by any means, no one can deny that it held a lot of history.
Sirius looked up at the bedposts, noticing the marks they had left, finding the ones they'd done on purpose in their human forms, the ones that form letters.
Moony, Wormtail, Padfoot and Prongs. Marauders forever.
Sirius traced the letters with his fingers, feeling the differences in the handwriting. James' was scratch and quick, Peter's deliberate, slow, but still messy, Sirius' own rough and sloppy and Remus'… Remus' careful, smooth and flowing handwriting.
Sirius closed his eyes and traced Remus' nickname, remembering the way he looked as he carved into the wood, nimble fingers delicately holding Sirius' knife, the smooth skin on his face wrinkled as he scrunched up his face in concentration, tongue barely poking through his lips… How could Sirius not fall in love with him? Based on looks alone, Remus was more than Sirius could ever ask for, and then he had an amazing personality as well. For a moment, Sirius was back in school, carving his name into the wood of the bed on the last night before graduation, laughing and joking with his friends, young and ready to go out into the world, fight for what's write and live happily every after with Remus and any pet but a cat. Two dogs owning a cat, well… it wouldn't really work out.
But then Sirius opened his eyes and that moment was gone. He was back to being a tired, run down ghost of his former self who was on the run from the law and alone, whose one true love probably hates him…
And at that moment, Sirius would do anything to go back.