Afterlife

Sirius & Remus {Pining, Onesided Wolfstar}

"You're pining, Sirius," James warned, watching as the man continued to dust the shelves that weren't dusty. "You're pining and you're ignoring it."

"I am just trying to clean this place up," Sirius replied. They were in the apartment that belonged to simply Sirius, who was living (dying) very much alone and single, as he constantly announced to everyone around him. And frankly, James was tired of this.

"Nope, you're avoiding the subject!"

"James," Sirius threw the cloth down and looked him very intently in the eyes. "I'm fine."

James hesitated for a moment, waiting for the flash. Because he could tell when Sirius was lying, and there was always a simply moment that screamed that he wasn't fine and then yep, there it was.

"Liar," he pointed immediately. "You're putting it off, you have been ever since Remus came."

"What have I been putting off?" Sirius asked monotonously.

"You've loved Remus since literally 4th year, so you hate the fact that he's married to someone that isn't you," James said very bluntly.

Sirius closed his eyes and took a deep breath, ignoring the weird tickle in his throat. "I loved Remus, yes, but that ended during Azkaban."

James snorted, "Sure, yeah, because I didn't find you in Harry's 3rd Year doodling Remus' name on a scrap piece of newspaper."

"People do that the whole time!" Sirius

"Yeah, with people they obsess over, like stalkers and stereotypical teenage girls in romance movies. If you're already alining yourself with them, mate, you're a goner in terms of this little chat."

"Shut up," Sirius turned away from James, sat on the sofa and blatantly looked at the ceiling when James sat next to him.

"It's okay," James told him. "Vent to me. I'm not going to blabber it all back to him."

Sirius felt the prick of a first tear and wiped it away angrily. "We...we were so good together. He was good for me, and he told me he loved me So Many Times in those last few years of school. But everything went to hell. I suspected him, he suspected me, it was a vicious cycle. And then Azkaban happened, and he was all I thought about. Remus, Remus, Remus. And the occasional 'I'm such a bad godfather, James is going to kill me' of course. I wanted nothing more than to kill Peter, with Remus by my side. And I tried, but your son, who is too good for Earth, stopped us. But Remus was still distant, somehow, disjointed from what we once were. That long in prison...it changed his opinion of me. I wasn't the same in his eyes. It got better over time, as we spent more time with one another.
"The summer of the fourth year of Harry's school and the beginning of fifth, I really thought maybe. Maybe he still has feelings for me. But then he dropped the bomb of Tonks, and before I knew it I was gone and there was nothing anymore.
"They got married, and I watched from here in agony. They had Teddy and it pained me even more. Teddy is so like him. But Remus...god, I don't think I'll ever stop loving him. Not that he will ever know, because you're sworn to secrecy."

"Wow," James said bluntly. Sirius' soliloquy took longer than he had expected, breaking his heart with the story of his friend. As time went on, it seemed to wear down at Sirius more, and now, he seemed broken at the thought of being alone.

Yet there was nothing, simply nothing, James could do to break the situation from stalemate except encourage Sirius to move on, something he adamantly refused to do, "or at least not for another few decades".
Remus was in love with Tonks.
Remus was married and had a kid. Remus was not in love with Sirius.
But Sirius was in love with Remus, and that was why the unrequited tale would leave Sirius pining for a man who no longer loved him.