Here's the epilogue. Hoorah. It takes place in OotP, in chapter 29 (Career Advice) when Harry's just seen Snape's worst memory and goes off to ask Sirius about it. Enjoy.
I'd like to re-iterate my disclaimer here and point out that I would never claim to own Harry Potter. If I ever made such a claim, they'd send me to the loony bin.
Remus paused, speaking slowly as he tried to explain why James and Sirius had continued to torment Snape even after they'd stopped acting so arrogant all the time at Hogwarts. "Snape was a special case. I mean, he never lost an opportunity to curse James, so you couldn't really expect James to take that lying down, could you?" Hopefully that made more sense to Harry than it did to him.
"And my mum was okay with that?"
Sirius cut in, "She didn't know too much about it, to tell you the truth. I mean, James didn't take Snape on dates with her and jinx him in front of her, did he?" Then his face lit up suddenly and he turned to Remus. "Moony, do you remember that bet we made in transfiguration once…" He whispered into his ear, "About giving you ten extra galleons if you tell Prongs's kid a certain something? I already gave you twenty when Harry was born."
Remus flushed and glanced at Harry, who looked (as usual) quite puzzled. "Well, Merlin knows I haven't got ten galleons to my name… and I suppose it's something worth knowing." He turned back to Harry and paused, thinking of how to tactfully raise the subject. "Er, Harry…"
"Out with it, Moony!" Sirius poked him in the chest with a mischievous grin.
"P—Sirius! Do you want to scar him for life, or shall we do this properly?"
"Do you want your ten galleons?"
Remus sighed with resignation, suddenly aware of how tattered his robes were as a draft blew in. "Fine… Harry, Sirius and I dated at Hogwarts."
"..And?" Harry looked even more perplexed now.
"Er… dated each other, that is. We had a bit of a parting just after you were born, but we're together again now." He felt Sirius's calloused hand creep over to hold his. "I hope you're not too entirely shocked," He added kindly. Harry looked back and forth between the two of them, as though waiting for one of them to burst out laughing.
"You still haven't said all of it, Moony…" Sirius winked, still holding Remus's hand.
"I was hoping you'd forgotten about that. Harry, did you know that there's this one particular corner of the Hogwarts library that's perfectly sheltered and devoid of people? You can get away with nearly anything back there." Harry looked uncomfortable, as if he didn't really want to know the relevance of that statement. "And, forgive me, Harry…" Remus paused with concern for the kid's sanity, but then plowed on with determination. "Sirius and I engaged in many, many immoral acts in that spot." He blushed and turned away nervously, focusing on a speck of grime on the floor.
"Is that Kreacher coming downstairs?"
"No," Said Sirius, glancing behind him. "It must be somebody on your end…"
"I'd better go!" Harry took off, looking more than a little relieved that he could leave without having to look them straight in the eye again. His head disappeared from the flames and Sirius immediately dissolved into giggles.
"That's not funny, Sirius, he could be really shaken! I'll send him an owl tonight… I hope he's ok…"
Ha, that was stupid, I'm sorry… But, on the plus side, I'm announcing plans for a sequel! Hoorah!