Just for a moment let’s think about Draco Malfoy, let’s think about how good he is at making paper birds and how he writes different things in them. And yes, we know that in the movies we only saw him writing a joke to make fun of Harry but let’s think of the possibility of him writing different things, like jokes, secrets or random thoughts. Think of Draco writing in the middle of the class and secretly sending a little bird to Harry with secrets and setting a time and place to meet where nobody would find them and where they can be the teenagers they are supposed to be without the pressure of being the "perfect pureblood" and "the chosen one"... And yes, I know. How can I say this is about Sirius if I’m only talking about Draco? We are getting there, just bear with me.
So, let’s say that this is a pureblood thing, that learning different skills related to art is mandatory and that is some weird tradition of pureblood families because all the kids need to be like dolls, flaunted in parties for the adult's entertainment, so if you are from a pureblood family you have to do it. It doesn't matter if you don't want to do it. You just have to.
And Sirius, the eternal rebel, the guy that hates his family to the core -with the exception of his little brother, because... "You would love Reg if you truly know him... and no, James, I'm not talking about the mask he puts on in front of our horrid parents, I'm talking about the real Reg"-. Well, he decides that he wants to learn to do paper birds and learn about flowers and really wants to do it, especially when he realises that his parents hate the idea of it because “something as delicate as learning about flowers and origami isn’t Black like at all, and you should be ashamed Sirius, for trying to act like a dainty pureblood lady”. But fuck them, and fuck their misogynistic ways. So, Sirius learns to do origami and learns about flowers and their meanings... and he likes to do those stupidly little paper birds and draw flowers and write their meanings in the folded corners of the origami he makes... until he arrives at Hogwarts.
No, Hogwarts didn't take that away from Sirius, but he doesn’t do it anymore. He doesn't need to do it anymore. After all, he hates his parents, not only because they are resentful of him for being a Gryffindor and not a Slytherin, but because he knows his parents' ways are incorrect and cruel, and he really thinks they are snotty fuckers that can get it for all he cares. So, he hates them and hates the idea of following any tradition that they forced on him, even if the paper birds and the flowers were his ideas to piss them off.
So he stops doing the paper birds and he stops learning about flowers or drawing them or writing about them...
He stops... until he falls in love.
Until he falls in love with this insecure dork that is the sweetest guy ever and who’s always thinking he’s a monster just because he’s a werewolf, though Sirius can’t help but think about him as the best thing that has ever happened in his miserable life. He falls in love with the nerd that is also surprisingly clumsy and that is always running behind Sirius and James, only to stop them or at least make them tone down some of the pranks Sirius' sick and twisted mind can create. He falls in love with the boy who apparently has an unlimited supply of chocolate and that is quite cuddly when it's raining outside. He falls in love and can't nor wants to avoid it, even if he's scared shitless with the idea because how dare he? How dare Sirius fall in love with someone so amazing as Remus when he doesn't even know how to describe love? But, he falls in love and doesn’t say a word about it, because, if he has to be honest... he doesn’t understand it.
Because his parents never showed him love or showed any love to his little brother, or even between each other. In fact, his parents seemed to be in a working relationship at best and a hate relationship at worst. Walburga, that horrid excuse of a mother, paid them no mind, only caring for their existence when she wanted the perfect heir to show off at pureblood parties or when she was so pissed off that she needed to curse something. Orion, a mere shadow in that awful house, a man pretending to be a father to two kids he barely knew, was like a ghost, uninvolved and cold in the place they dared to call home. In this house, love was a foreign concept, a distant memory that had long since faded away, that's it if it ever existed in the first place. The only love that he ever knew was from his brother. His little Regulus. The only person he even dared to love with such intensity, and sadly, now their interaction barely existed, between his brother pretending to leave him behind as soon as he was placed in Slytherin, being forced to follow their parent's footsteps, and Sirius being obligated to pretend that he hates Reg so Walburga wouldn't hurt him...
So he starts doing paper birds again because he is good at it and because doing paper birds is the only thing that he likes about his family’s traditions, even if he was willing to throw that away to go against his parents' mere existence... So, he writes love letters, draws little flowers with their meanings written in a small and barely readable font and lets his quill move over the paper, flooding it with different thoughts about this dumb and wonderful boy, that makes his heart rush and beat with happiness and nervousness.
He doesn’t send them, because he doesn’t like the idea of ruining the friendship with this boy, so he goes to the astronomy tower and with a pretty easy spell he lets the birds fly away and sees them while they disappear in the middle of the forbidden forest. He knows nobody would find them, and if someone does, nobody would know that those little birds that contain all his feelings and secrets belong to him.
A couple of years later, after a lot of pushing and pulling and after James threatens Sirius to yell about his crush with Remus in the Great Hall if he doesn't do something about it, Sirius confesses to the sweet werewolf and they begin to date... So, Sirius stops doing paper birds again. After all, he doesn’t need to hide his feelings from this boy because he can tell his boyfriend that he loves him and this fantastic guy won’t run away and will actually say it back.
So one day, years after the confession, years filled with love, fights, making up and just being so loved... they are cuddling on their couch, just watching some movie in this muggle artefact, called television -even if Sirius still calls it by the wrong name- because: “This is crazy, Remus, sometimes muggles create the most amazing things” and “It’s just a tv, Sirius…” and they are having a really great time, Sirius doesn't really understand the movie, but his cute boyfriend likes it so the black-haired wizard can take a moment and watch the tv while he admires how Remus reacts to the film, even if the werewolf has seen the movie four times every year since they got the tv... But then Remus is cold, so Sirius stands up because if Remus is cold, Sirius is going to get a blanket for him. After all, Sirius is a good boyfriend and he won’t allow the love of his life to get sick.
So, without pausing the film and letting Remus keep watching the tv, he walks out of the space until he’s in their bedroom and while he grabs the blanket he was looking for, a box falls off the shelf and opens as soon as it drops on the floor, spilling all the content all over their carpet. So Sirius grabs some of the paper birds that are now laying around because even if he doesn’t remember writing so many, he recognizes his little flower drawings everywhere and these paper birds are filled with those silly doodles. Sirius opens one of the birds and reads the letter inside.
He spends the next hour reading them all.
After a while, Remus goes to their room, joking about Sirius getting lost inside the closet even if he already came out, but sobering up when he finds the other boy, hugging every bird while he cries like a baby. Shocked by the deep emotions that carried each one of these little confessions and doodles, neatly folded with caring hands and a bleeding heart.
At that moment, Remus hugs him and just waits there until Sirius feels better, not saying a thing to avoid interrupting this moment. Because Remus will do that, Remus will treat Sirius carefully, with kindness, with small kisses and soft hugs, Remus will comfort Sirius when he feels down or when he gets overwhelmed with emotions that he can't begin to explain, because Remus loves Sirius and because Remus is the guy who, in all the little birds, with a neat font and so much adoration in his heart, answered every single letter and thought with a simple “I love you too, Sirius”.