a/n: blainchelcest with blam and faberry written for a friend :3

It all started the day the Fabray twins moved into town.

Really, it probably started a year or so before that, the day he and Rachel sat in their basement watching some movie while she complained about how lackluster Finn was in the kissing department, Blaine trying to focus on the movie and less on his sisters hand as it kept landing on his thigh. "I just thought it'd be something more, you know?" she asked him, looking up at him with those wide brown eyes he never found himself saying 'no' to.

He wanted to tell her he did know, but the truth was he hadn't really had the 'more' either. His experience was limited to some jackass from Dalton who left him within weeks, their relationship losing all the fun for him as soon as Blaine started latching on, despite both their desire to keep the fling a secret. The kisses-and more-he had shared with Sebastian were nothing to keep coming back for, and from Rachel's complaints it seemed she had the same deal with Finn.

Not that he was shocked, because Finn was kind of an idiot and probably didn't know how to put up with his high maintenance sister, much less kiss her the way she wanted. How that equated to Blaine finally giving in with a sigh and kissing her himself, he didn't know, but he couldn't find a complaint as she scrambled into his lap, their lips becoming chapped and red as they spent an entire afternoon leaving their classic movie behind and becoming lost in each other.

It became a regular thing, and the secrets Blaine was keeping kept adding up. Incest, he knew, was far more frowned upon than the whole 'gay' thing, but even that was confusing when he added into the fact that he was regularly spread underneath his very girlish sister, coming undone under her hands and mouth and body on a regular basis. It was easier to keep everything hushed, to have friends and not search for anything more, to quell any jealousy he may have ever felt towards Rachel's ridiculous relationship with Finn Hudson. He had never been so relieved as the day she finally told him goodbye, for the last time, sending him packing and leaving her with no one to focus on but Blaine for the entirety of their summer vacation.

Not that Blaine minded.

But the second their junior year started, there was a new set of siblings that seemed destined to take over the school. Not that he and Rachel ever really had, Rachel running her show choir and drama club while Blaine just migrated between groups of people, spending most of his time with either his sister or Mike Chang, but the Fabray twins were nothing like that. Quinn, the girl, somehow jumped ahead of Santana Lopez and made Cheerio captain by the end of the first week, Sam, the boy, winning the role of quarterback over Finn at the same time.

Blaine could tell Rachel had set her sights on the blonde, narrowing in on him and asking him to join the New Directions under the guise of needing new members when she saw him playing guitar over lunch one day. He had smiled at her, easily and friendly enough, Blaine's stomach swooping slightly at the sight, and he didn't know who he felt more jealous of-Rachel for Sam's attention, or Sam for Rachel's.

It turned out that it didn't matter, not really, as the two were dating and nearly inseparable within another two weeks. Sam was constantly around their house, Blaine catching his sister's bossy demands before hearing Sam's chuckles in response while they practiced for glee, tortured by sounds he had heard fall from Rachel's mouth under his own power too many times to count, by new ones that had a distinctive male sound to them and he didn't know which made his hand wrap around his own dick faster, leaning against the doorway of the bathroom he shared with Rachel and eavesdropping on his sisters mid-afternoon sessions with Sam.

She caught on quick enough, once the novelty of sleeping with someone new seemed to have worn off and she started crawling into Blaine's bed again, and it didn't take long before she started telling him all the various ways Sam felt against her skin, inside her mouth, in the palm of her hand. How his mouth, almost obscenely large in size was perfect for traveling across her body, and wouldn't Blaine like it to travel across his own?

He wanted it, bad, but he wouldn't admit it aloud and instead decided to take a route of action he was entirely unsure about, approaching Quinn and asking her out on a date the following evening to which she readily replied.

It was easy and simple dating Quinn, she simply wanted a rise to the top of the social ladder and with Blaine's many connections throughout the school, he could provide that to her. He was talented and charming and classically handsome, and their time alone was rarely spent doing much besides schoolwork. The truth was, he wasn't really attracted to Quinn, not like he was Sam or even Rachel, and he was rapidly coming to the conclusion that she wasn't all that attracted towards him, if her lingering gazes in his sisters directions gave any indication.

It was almost bemusing to him, that he'd be dating the girl who was in love with his sister while his sister dated the boy he was in love with, if it wasn't sheer torture for them to all pretend that it wasn't exactly like that. But as his sisters eyes traveled over towards Quinn more and more often, Blaine started to wonder just what it was they were all doing. He supposed it could be repressed jealousy of the blonde, though when Rachel had confronted him, Blaine had told her straight up that their relationship was a bigger sham than hers had been with Finn.

Still, no one seemed to make a move until he opened the door one day to find Sam standing on his doorstep, confusion coloring Blaine's features as he informed him that Rachel was out for the afternoon.

"I'm not here for Rachel," Sam said simply, looking almost too sure of himself but Blaine had no time to question him further before Sam crashed his lips onto Blaine's own, a sound of surprise hushed by the pink tongue chasing into his mouth a moment later.

Blaine had heard all about Sam's style and technique from Rachel, who often complained that he treated her too nicely, too daintily, as if she might break. "He's a gentleman, Blaine, and that's not what I want," she'd told him too many a time before making Blaine do the exact opposite of everything she was getting from Sam.

But Sam was nothing like that with Blaine, pushing him against the wall near them so hard a picture frame crashed off of it, Blaine glancing at it momentarily before the blondes lips suctioned themselves to the tender spot underneath his earlobe, causing Blaine's hips to jut forward and into Sam's. He heard a whisper of 'fuck', but it didn't seem to come from Sam any more than it had Blaine, and with regret he looked towards the front door to see Rachel standing there with wide eyes.

"I can-" Sam started, but Rachel just shook her head 'no' before slamming the front door on her way out, Blaine pulling his shirt back down from where it had ridden up and Sam muttering about what an idiot he had been.

"She's not upset with you," Blaine told him warily, because he couldn't be sure about anything at the moment, except on his suspicions on where Rachel was disappearing to right about now.

"How could she not be? She just walked in on me making out with her brother!" Sam cried out, sounding far more distressed than Blaine thought was ultimately necessary, and Blaine just chewed on his lip while Sam panicked, yelling about what a dick he was and how he had fucked everything over for everyone.

It would have been an opportune time to mention that Rachel wasn't exactly innocent from cheating herself, though Blaine didn't know how well Sam would take it to hear that she'd been cheating on him with her brother of all people, and instead decided that actions spoke infinitely louder than words as he pulled Sam back into himself, Sam only hesitating briefly before they resumed their frenzied rush of hands and mouths moving across one another.

When Rachel came in that night and apologized for freaking out at him, a new hickey on her hip that hadn't come from either Blaine or Sam, Blaine could only smirk in response with a raised eyebrow. "Quinn?" he questioned, a flush crawling over her cheeks as she nodded.

"It seemed fair," she responded evenly, Blaine laughing lightly as his fingers trailed over the mark.

"You always did believe in an eye for an eye," Blaine replied, Rachel hitting him playfully before snuggling deeper under the covers on his bed. "I don't think I can stay away from Sam," he told her truthfully after a moment, Rachel popping open an eye and staring at him intensely.

"I don't think I can stay away from Quinn," she finally answered, Blaine nodding in response.

"I suppose this isn't the worst thing we've agreed upon," he said, Rachel letting out a soft laugh of her own as her hands wound around his waist, pulling him closer to herself.

"No, Blaine, I think stealing each other's dating partner is hardly the worst thing we've done together," she agreed, placing a tender kiss on the center of his chest. "I just don't want to know about it, okay?"

"I know how you feel about sharing," Blaine reminded her, words muttered against the top of her head as she settled in for a long nights sleep, his breathing seemingly steadier for a few quiet moments.

Sometimes, he figured, you were given the chance to have your cake and eat it too. And he was never one to back down from a golden opportunity.