Disclaimer: These characters belong to J.K. Rowling and are used without permission
Notes: WARNING: SLASH. I do not own a copy of PoA, so if this is canonically incorrect, please let me know and I will fix the problem. I'm not sure if it's necessary to say this, but this ficlet is based more on book canon, where pretty much the whole DA can produce a Patronus, rather than movie canon with that "really advanced wizard" thing.
Remus used to be able to produce a full Patronus.
It looked like Padfoot, and he'd been embarrassed as all hell the first time everyone saw it, but once he got over the blushing he'd looked up to see Sirius with a sheepish sort of grin, one he'd never seen on his friend before, and that night as they held each other, Sirius had whispered "no one's ever expected me to protect them before" and Remus had felt much better about the whole thing.
The memory he used was the first time Sirius had kissed him, when he'd whispered furiously in Remus's ear "It doesn't matter what you are, I love you, it doesn't matter it doesn'tmatterIloveyouIloveyouIloveyou." It was, by far, the best memory Remus ever had, and the Patronus it produced was strong.
Then Sirius went to Azkaban, and Remus's Patronus was reduced to small bursts of light. Every memory of Sirius only brought pain (it wasn't fair, Remus had always thought, Azkaban was supposed to take all of Sirius's happy memories away, it wasn't fair they'd taken his too) and any other memory he had simply wasn't strong enough.
His Patronus worked well enough, he guessed, and it wasn't like he often encountered dementors in his everyday life, so he tried not to think about it. It worked, mostly. After about the seventh year, he'd mostly forgotten how good it had felt to be with Sirius, and so the pain was lessened by that.
But he had come back. Sirius had come back and it was like all the memories had come back with him. Lupin felt safe again, and though he had no dementors to face, he was quite sure that if there was one, his Padfoot Patronus would be there to defend him. He spent two years like this, two years where nothing really mattered except that he had Sirius back. Everything would be alright. Remus believed this fervently. It would be okay, everything would end up set to rights in the end.
And then Sirius died.
And Remus stood in an empty room in 12 Grimmauld Place, and over and over he yelled "Expecto Patronum!" and over and over only light came out of his wand. He was desperate to see Sirius again, desperate for anything that looked like him, even if it was just a magic trick, but the happy memories were gone again, and Remus didn't think that they'd be coming back this time.