Understand.
James cared deeply for Sirius. At first James loved him as a best friend, then it was as brothers, then he finally understood that summer that he loved Sirius.
James was in love with Sirius Black. It was a hard pill to swallow so he didn't. He ignored it as much as he could, which was hard. Extremely Hard.
James loved the way Sirius used his wand to put his hair up, he loved the way Sirius expressed himself through what he wore, he loved his taste in music, he loved when he wore crop tops, he loved when he wore his bellbottoms or ripped jeans, he loved when he wore his leather jacket that James himself got Sirius, he loved how Sirius looked so peaceful when he actually had a good night of sleep, he loved spending time with Sirius, he loved that mischievous grin he got, and he loved his piercings, he loved how he snorted when he laughed, he loved that Sirius would steal his clothes (and got jealous when he stole anyone else's so he would purposely leave his out so Sirius would steal his), he loved the eyeliner and make up Sirius would wear, he loved his curly hair, he loved the color do his eyes, he loved how he sounded, he loved his laugh, he loved that Sirius would give them small gifts, he loved his personality, he loved when. Sirius would point out stars when they went star gazing(Sirius always points out Regulus' star). He found it adorable how he loved animals more then people but was extremely good with people, how he was so good at puzzles, how he wiped his feet off before getting in any bed, how he screamed when there were bugs, how he kinda always stood in ballet poses(which made James call him a ballerina), when he said the most unhinged things ever whenever it got silent.
Oh Merlin he loved Sirius Black.
He thought he could never feel anything other than love for Sirius.
Oh how James wishes Sirius wasn't cursed by the last name Black.
...
Sirius always knew he was in love with James Potter, he didn't hide it, the only person who didn't know was James.
He would always yearn, ache, and long for him, he was irreversibly, out of his mind in love with James Potter. Which made 6 years of pining hurt more than anything in this world.
It hurt when James would talk about Lily Evans, it hurt when James smiled, it hurt when he laughed, it hurt when he was kind to Sirius, it hurt when James showed him warmth, it hurt when Sirius looked into James eyes(that was the first thing Sirius fell in love with), it hurt when James went out with other people, it hurt when James would simply spend time with him, it hurt when James would comfort him, it hurt when James complimented him, it hurt when James found interest in what he had to say, it hurt when James speaks with his lovely voice, it hurts when he teases him, it hurts when he looks peaceful when he sleeps, it hurts to look at him when he dresses in comfortable clothes, it hurts when he covers his ears when parties get loud, it hurts when James takes care of him when he gets to drunk at a party.
Sirius understood what it meant to love now, and it ripped his heart out, love was brutal when unrequited, it would tear you open and slam you down to rock bottom, it will show you everything, it will make you hate yourself and your imperfections, it will make you do things you would never normally do, every form of love in his life hurt so bad he didn't want love. But never in his life will he regretloving James Potter, it hurt, but the burn felt good sometimes.
Oh Merlin it hurt to love James Potter.
Sirius Black is always going to be in love with James Potter no matter how much it hurt.
Oh how Sirius wishes he wasn't cursed with the last name Black.