Remus Lupin always knew Sirius Black would break his heart.

He'd known it the first time Sirius had looked at him on the train: a dark-haired, boisterous boy of eleven with sharp grey eyes and a wide, smiling mouth. He had seemed to Remus to be an angel – pretty, loving, but distant, incalculable and in some ways cold. He had watched as Sirius had clambered onto the seat beside James, all elbows and flailing limbs, not at all the movements one would have expected from a boy who almost exuded grace and elegance.

Hello, Sirius had said, peering out from under black hair that fell almost artfully around his face, I'm Sirius. What house do you think we'll all be in?

Remus Lupin always knew Sirius Black would break his heart.

He'd known it during fourth year, when he'd spotted Sirius emerging from one of the school greenhouses with his latest girlfriend. It had seemed to Remus, then, as he watched them walk back towards the castle, trading touches and the occasional kiss, that a giant fist was squeezing his heart, making it painful to breathe. He had turned away, panting for breath and desperately trying to figure out why he wanted to wail out loud.

Remus Lupin always knew that Sirius Black would break his heart.

He'd known it even as Sirius had stared at his hands, head bowed so that a curtain of black hair hid his beautiful pale face. Sirius had refused to look at him as he spoke softly, haltingly, and it wasn't until he'd finished and the silence was stretching on almost unbearably, that Remus had reached out and lightly touched the top of Sirius's head. His body had been trembling, but he managed to keep his fingers firm as he watched Sirius look up, surprise and uncertainty ill-suiting his face. A joyful, uninhibited grin had broken out, then, and Sirius had stared at him with star bright eyes, mouthing those three little words.

I love you.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it when James had appeared by his bedside the night after the full moon, his face full of regret. There's been an…accident, he'd said, not quite meeting Remus's eye. Remus hadn't needed more than that. He'd known. Sirius, it all came back to Sirius, who, despite everything, continued to hold Remus's heart. He hadn't wanted to accept the truth for a while: Snape, the Willow, Sirius… but it all made sense in a horrible, twisted way and it had taken Remus the best part of a year to forgive Sirius.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it even when he'd moved in with Sirius after they'd left school. Come with me, Sirius had murmured against his mouth as they lay in the hot sunshine of early morning. Live with me, Moony. You won't regret it, I swear. Like a fool, Remus had believed him. He'd packed up his books, his clothes, his very life and taken it with him to Sirius's flat. 'No regrets,' he'd thought at the time. It was vital to live for the moment and not worry about the consequences that lurked in tomorrow. Sirius was there and he'd been content with that and that alone.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it when Albus Dumbledore appeared on his doorstep one rainy morning, dripping on the new rug Sirius had brought back from Persia not six months ago. He'd realised that there was no other choice but to let the man in, and the news had been received with a numb shock that spread from his heart – radiating outwards until his whole being felt cold and distanced. Sirius was a traitor. He was blind not to have seen it, but his unfaithful heart had covered up Sirius's imperfections – to Remus he was perfect and the possibility of this side to Sirius had not truly crossed his mind. He hated him and loved him all at once.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it the morning he'd picked the Daily Prophet up from his doormat only to discover Sirius staring back at him. He'd moved about the house in a daze that day, half dreading, half expecting the letter from Dumbledore that arrived that evening by post. It offered him a position as Defence Against the Dark Arts teacher. He accepted willingly, despite the obvious implication underlying this generous offer – that he could not be entirely trusted not to help Sirius, now that he had escaped from Azkaban. Old habits, Dumbledore had written, and old loves, die hard.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it as Sirius stared up at him from the floor of the Shrieking Shack. He had been skeletal-thin, his clothing ragged and patched, his long dark hair trailing in the dirt and the dust, but he appeared to Remus so wholly alive, so utterly Sirius that he recognised at once why Dumbledore had made sure he stayed at Hogwarts. Sirius was not only his love, but also his obsession and as Remus pulled him up for a fervent, desperate embrace, he had felt Sirius's hands clutch convulsively at the front of his robes – as desperate to hold onto him, as he was to hold onto the convict.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it when the doorbell had rung one cool night in June. Putting down his book he had opened the door, only to discover a familiar dog sitting on the step. He had paused, stared for a moment, drinking in the sight of Padfoot, before stepping back, letting Sirius into his only sanctuary without a second thought. With an open house and open heart, he had made tea and sandwiches, thinking first of Sirius's ferocious appetite. Sirius had watched him, drinking the steaming tea from the mug, not even wincing, as the hot liquid no doubt burnt his tongue and throat. Later, Remus's tea had been left on the side, slowly turning cold, as he lay upstairs in bed next to Sirius, soothing his nightmares and patiently chasing away the lingering shadows of Azkaban.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it when they'd moved into Grimmauld Place. He'd watched, despairingly, as Sirius had reacquainted himself with the house he had run away from in his childhood. He had patiently submitted to listening to Sirius's complaints about the dust, the spiders, Kreacher, the spiders, his mother's portrait, the spiders, the man-eating rug…and the spiders. They had both laughed when, one afternoon, Sirius had discovered an old apron in the kitchen and had insisted on wearing it for the rest of the day as he did the spring cleaning, wand in one hand, feather duster in the other. Remus had managed to make one joke about the 'French maid outfit' (as it was dubbed), before Sirius had flicked the duster at him, earning swift retaliation with the mop. What had followed was an all out cleaning appliance war, which had ended in a staggering, frantic flight to one of the clean bedroom.

Remus Lupin always knew Sirius Black would break his heart.

He'd known it as he watched Sirius's newfound love of life slowly fade and dwindle under the never-ending pressure of living in the house he loathed. He ignored the sympathetic looks of the other Order members, who clearly thought he only put up with Sirius's moods because of their friendship, and he made sure he hid the firewhiskey before he left on any work. It wasn't that he didn't trust Sirius – he did – but he knew what depression could do to a man and how, eventually, alcohol consumption begins to look an incredibly tempting way in which to solve your problems.

Whenever he came back, Sirius would always kiss him as though it was the first and last time.

Gratefully, a small, pleased, treacherous voice would say at the back of Remus's mind.

Remus Lupin always knew Sirius Black would break his heart.

He knows that Sirius is dead. It is obvious by the sudden, shocking, Sirius-shaped hole in his life and the way his scent lingers on pillows he will no longer sleep on. Remus's mind tells him the facts that his heart refuses to accept. He continues to exist, merely because it is required that he do so, and he can feel the same numbness creeping over him that he experienced when Sirius was arrested for killing Lily and James. It's shock, the other Order members murmur to one another, he's lost his dearest friend. It's to be expected. He'll come around eventually. Only Tonks watches him with eyes that are too old for her young face – eyes that hold some measure of understanding. She notices the way Remus throws himself into his work – trying to ignore what has happened.

She finds him, some three weeks after Sirius has died, staring out of one of the top windows of Grimmauld Place, blood streaking his hands. A smashed vase lies nearby and he is shaking as he rests his forehead against the glass. Without a word, she puts an arm around his shoulder and leads him back downstairs.

Remus Lupin always knew Sirius Black would break his heart.

He just never expected it would be like this.