A/N: Originally written for westwardlee on LiveJournal for hp_toujours 2009. Contains infidelity and a brief description of a sexual encounter between two teenage boys. Heed the rating.

Fidelity in the Eye of the Beholder

"Good game."

Regulus looked up from his broomstick. He'd been idly polishing it for ... well, he'd lost track of the time, but the rest of the team had changed and gone back to the common room, and here he was, sitting in the changing room.

"We lost," he said. "What's supposed to be good about that?"

"You caught the snitch."

"I had to save what little dignity we had left. Can't believe we lost to bloody Gryffindor..."

James grinned. "Didn't just lose. You got well and truly trounced. Two hundred and ninety to one hundred and fifty..."

Regulus got up and finally started packing his gear. "Go fuck a niffler, Potter."

"I have a better idea."

Regulus glanced over at him with a raised eyebrow. "I'm not fucking you right after you beat my team at Quidditch. Besides, shouldn't you be off having a celebratory shag with your girlfriend?" He packed up the last of his gear, threw his bag over his shoulder and turned around, only to find James blocking his path. "Seriously, Potter. I'm not interested." Which wasn't, strictly speaking, true. He was seventeen and always interested, but the game hadn't put him in the mood to deal with James right after being knocked out of the running for the Quiddtich Cup.

He wasn't quite certain how he got into this situation in the first place, this arrangement with James Potter, but it was all James's fault. James, who'd been all sweaty after a long afternoon flying, who walked around the changing rooms naked so that people like Regulus couldn't help walking in to a perfect view of that arse, toned from hours upon hours of Quidditch practice, clutching a broomstick between his thighs...

And if James had seemed at first a little uncertain about bending over and bracing himself against the lockers while Regulus took him from behind ... well, he'd certainly embraced the idea since then.

The trouble with James was that he was too bloody charming by half. He had that stupid, overconfident smile, and that glint in his eyes like he knew he could get Regulus to do almost anything if he found the right way to ask -- and he knew that finding the right way was only a matter of time. And when he asked ... when he asked, it was with kisses that were too forceful and a little clumsy, too much teeth and tongue, wonderfully unrefined.

Regulus was sure that whatever horrid little pure-blooded bitch of a wife he ended up with wouldn't kiss like that.

He reluctantly pushed James back for a second to gasp for breath and ask, "How long before someone comes looking for you?"

"A while," he said. "I told them I was going to Hogsmeade for Firewhiskey."

"Lying to your friends so you can cheat on your girlfriend?" Regulus grinned. "Very Slytherin. I like it."

"I am going to bring back Firewhiskey, so it's not really lying," James said. Then added, "And it's not really cheating."

For a moment, Regulus was silent. Then he shook his head and a wry smile pulled at the corners of his lips. "Never mind. Definitely a Gryffindor. Because you actually believed that when you said it. Wanted to, anyway."

Regulus knew he'd hit a nerve when James's jaw tightened and his eyes narrowed. "I didn't come back down here to talk about my life, Black."

"Good," Regulus said as he pushed James back against the lockers, "because I have very little interest in anything you have to say."

The first time they'd done this, James had been startled when Regulus pinned him against the wall. His eyes had been wide with panic and his face flushed when he realised that one hard, Quidditch-toned body pressed against another could provide the most delightful friction.

He'd just started dating that Evans and Regulus quickly realised that, like most Gryffindors, Potter did a brilliant job of rationalising his sins away. He wouldn't top -- that was cheating on Evans. Bottoming, on the other hand, was completely unlike anything he did with her. That was okay. He wondered in a passing sort of way how James justified both giving and receiving head, but he never asked. Maybe Evans was the sort of prude that didn't go down. Maybe blow-jobs just didn't count. Regulus didn't much care.

And he didn't question the logic. He wasn't picky, and either way, he got off. And James did look fantastic after the Gryffindor win, braced against the walls of the shower, thighs parted, fingers curling against the tiles that tossed his moans back as echoes.

As he pulled his clothes back on, he was quiet. "Am I awful ... for what I do to Lily, I mean?" he asked right as Regulus slung his bag over his shoulder again.

"I've no idea what you do to her," Regulus said. "I don't want to know."

"I mean sneaking around behind her back."

Regulus shrugged. "I thought it wasn't cheating. Isn't that what you said?"

"Is it?"

"Potter..." He didn't want to have this conversation. He didn't want to think that much about James's life outside of these quick trysts in the Quidditch changing room or, very occasionally, an abandoned classroom. "I'm not your girlfriend. I'm not your boyfriend. I don't care who you sleep with. It doesn't matter to me. I couldn't give a pile of pixie shit about the ethical considerations of your sex life. You're not cheating on me." He was about to turn for the door and begin the trek back to the castle when he saw the lost expression on James's face. He sighed. "Would she call it cheating?"

James didn't say anything, but the look that crossed his face said enough.

"There's your answer, Potter." He grabbed his broom. "I'll be studying in the empty classroom on the third floor on Thursday night. In case you wanted to know. But if you come, do me a favour and leave the guilt somewhere else, because I really couldn't care less."

And as he headed across the lawn toward the castle, he told himself he wouldn't be disappointed if James didn't show up. He wouldn't.