A/N: Yes, this is a Sirius/Lily pairing. Yes, this does involve Lily Potter being unfaithful to her husband James. That being said, no, James is not portrayed as a villain. If this is not your thing or you're easily offended by fictional adultery, just don't read (or comment!)

But if you do enjoy this pairing, I would be thrilled to hear all of your thoughts and feedback!

Disclaimer: Harry Potter is not mine, nor are any of its characters. *silently weeping*

Lily stretched and purred, squealing as her arms reached the height of their arch, shoulders extending almost out of her lean, muscular back. She was naked, of course, and the sun streaming in from behind the lacy white curtain was just barely brushing her tangled, tawny hair. she let out another little groan and let her arms drop, the bend falling suddenly out of her back. Long strands of hair fell over her shoulders and forehead, leaving her back tantalizingly exposed to the grinning, wild-eyed man lying back leisurely on his pillow with hands crossed behind his head, the gauzy white covers bunched low to reveal his chest in all its naked glory.

The man reached one long, strong finger across the bed to trace the lines and crevices of Lily's back, and she shivered at the warmth and delicacy of his touch. Without pause, letting the covers fall and his playfully predatory grin spread wide, he brought himself up to his knees, wrapping himself around the gratefully trembling woman from behind. She let her head fall back with a light sigh and airy giggle as he buried his head beneath her hair to lightly nuzzle her neck. She turned gently out of his embrace, her electric green eyes immediately holding him captive.

"Always the puppy dog, Sirius." She was grinning, those huge green eyes swimming in glee and mirth, overwhelming him with the pure, clean, innocent joy that was Lily Potter. He let out a short, gruff laugh and let his eyes fall from hers, escaping breathlessly from her spell before he became too trapped.

Laughing again in wonder, he let himself drop back onto the bed, now totally uncovered, staring at the ceiling with starry eyes. The change of weight on the bed told him that Lily had moved to get dressed, but he was still hesitant to move. He couldn't bring himself to end this moment of total satisfaction. Happiness. Weightlessness.

The bed shifted once again, and Sirius turned his head slightly to see a silk bathrobe-clad, beaming Lily Potter hovering over him. He whined slightly in the back of his throat and narrowed his eyes accusingly at seeing her covered up again, but she only giggled and leaned down for a melting, she's-doing-all-the-work, bracing, passionate, apologetic comfort-kiss. When she drew herself up again, her lips were slightly blushed and her eyes were gleaming even brighter. She looked distinctly angel-like covered in pale blue silk in the early morning sun, even if her husband had bought the robe for her.

"See you next Tuesday?" He sounded like a child, he knew, but he was so caught up in her eyes, her hair falling across her vision, her lips still swollen from last night's merciless, impassioned kisses that he couldn't bring himself to care.

"Of course. Did you really think I'd let you miss James's signature grilled salmon? Dumbledore's bringing strawberry crepes, apparently." She was gathering her clothes and toiletries, cramming them here and there into her green and brown knit bag, which had been a birthday gift from Ted a few years back.

Sirius continued to watch, un-moving, from his place on the bed. He watched her as she went to the bathroom to brush the tangles from her hair and charm the whole massive mess of it back into a braid. He watched her as she brushed her teeth using his toothbrush (hers was packed) and lightly apply his favorite light pink lipstick. He watched as she sent a patronus message to James to tell him she was on her way back from Petunia's, wincing as he watched the silver light take the shape of a doe. He watched as she pulled on a pair of simple jeans, a washed yellow tank top, and a green hoodie, smiling slightly when she peered over her shoulder at him as she let the robe fall to his floor. But finally, he watched as she walked to him to peck his lips good-bye, whispering a sweet, quiet "I'll miss you" into his ear before grabbing her bag and prancing out of the room, shooting one last smile back at him as she closed the door behind her.

For a moment after she left, he had half a mind to chase her down the hall, completely naked as he was, snatch her up, and carry her back to bed, and neighbors be damned. He always wanted that. Hell, who wouldn't? But there were things to do. He couldn't just keep lying here with his morning glory completely and thoroughly displayed to his married girlfriend's sister's apartment.

He chuckled again as he pulled himself grudgingly off the bed and scrambled around for his wand so he could charm the bed to begin making itself. It wasn't any kinky idea of his or Lily's, using Petunia's apartment. It was just a perfect coincidence - she was almost never home, especially on the weekends, it was an incredibly romantic, gauzy, airy loft, and meeting here meant that Lily was never really lying to James, and if he was ever to track her broom magically or call the loft on a muggle phone, they wouldn't have to dig themselves out of a horrible, hairy mess.

But that also meant that once every two or three weeks, sometimes on very short notice, Sirius had to pack a bag and set his life on hold to move somewhere in Muggle London. Not that he minded. Not that there was anything he wouldn't do for this girl.

So Sirius put on some clothes, packed his toothbrush and his towel, and looked one last, loving time around the room before closing the door and locking it. Hiding it, locking it away until the next time she needed him. The next time they needed each other.