Lilly was getting ready for bed, stripping down to her underwear bottoms. If her brother were there, she might've bothered with a t-shirt, but tonight she had the room to herself. Brian was in the next room over, spending the night with Emily; Lilly could hear plenty of it through the thin apartment wall in between, whether or not she wanted to. She had her earplugs handy in case she needed them.
Beth knocked and came in. "Hope I'm not interrupting. Can I spend the night here?"
"Sure," Lilly said. "I won't turn away a sexile."
Beth had to sleep somewhere after all, since her bed was in the room Brian and Emily were occupying tonight.
Beth sat down on Brian's bed. Lilly was still topless but she didn't bother covering up; everyone in the house had seen each other in various states of undress plenty of times already.
"We could probably split up the other boys if you want," Beth said, motioning to the third bedroom of the apartment, where Mika and Tyler were probably playing video games. "Or heck, you and I could mess around."
"No thanks. Not tonight," Lilly said. "I've got work early tomorrow. Those Christmas presents don't wrap themselves. But hey, if you want to sleep with one of the guys, go right ahead. Have them both, if you want. I won't feel left out."
The two girls sat together in silence. Well, not complete silence. Through one wall, they could hear Emily and Brian making out and muttering to each other. Through the other wall, they could indeed hear Mika and Tyler playing a shooter.
"I'll leave the boys to their video game," Beth said with a laugh. "I hope you don't mind the soundtrack, living here."
Lilly shrugged. "I knew what I was getting into. Like you told me from the start, radical free love. Anybody can have sex with anyone else. That's the rule."
"That was before your brother joined," Beth said. "I know you had...reservations about it."
"I did, at first. But then, once I got over myself, it made sense. He'd been hanging out here all the time anyway, spending the night with Emily. And it is a lot simpler to split a three-bedroom apartment six ways."
They heard Emily's cooing moan rise, and Brian started to rhythmically grunt. It was no secret what they were doing. As chill with it as Lilly tried to be, she found that the sound of people having sex always got her aroused. That part of her brain didn't seem to care that one of those people was her brother.
She was just starting to wonder how long this was going to go on, when Brian's grunts suddenly turned into a drawn-out groan. Emily's cries trailed off.
"Well, that was quick," Lilly said, keeping her voice low.
Beth struggled to keep her laughter quiet as well.
It wasn't long before the couple next door quieted down for the night.
---
The next night was a Friday, and the whole household was sitting around drinking together. Outside, it was a cold winter's night, the wind rattling the windows. Inside, the three-bedroom apartment was on the eleventh floor of a high-wise with thin walls. Heat rose through the building, making the apartment sweltering hot.
They were all wearing as little as possible. Lilly wore a t-shirt because her brother Brian was around, but she was starting to regret the decision as the beer warmed her up. It didn't help that she was leaning against Tyler's broad chest.
It was Lilly's turn to make a toast, and with her inhibitions a little loosened, she raised her glass and said, "To my little brother, for finishing fast last night so I could get a good night's sleep."
The room erupted with laughter, from everyone but Brian. Even Emily, her arm draped around Brian's neck, couldn't help but smirk.
Mika asked, "Oh, so the siblings finally did it?"
This made everyone laugh again, except Brian and Lilly.
"Gross," Lilly said.
"In my defense, it was my first time without a condom," Brian said. There were gasps around the room. They were all in the habit of using them.
Emily blushed. "Hey, what's the big deal anyway? I just wanted to try it out. It's not like either of us could get an infection from it. We're a closed circuit, right guys?"
"How far back are we talking? Because there was that time six months ago..." Tyler began.
"We get it Tyler. You're a slut. We all are. That's why we're all here, after all. To have a safe outlet for that," Beth said.
Beth was the leader of the group. It started with her and Tyler and Mika, renting the three-bedroom place for their poly triad. Then Lilly joined, and then Emily, and then Brian joined last. He started coming by to visit his sister, and eventually Brian was spending enough time there (mostly with Emily) to start paying rent.
Beth took a swig of her beer before she spoke again. "Actually, I was thinking, maybe we should help the guys out. So that they're better prepared for these exceptional occasions."
Beth gave Emily a stern look. Beth had tried birth control and had a bad reaction to it, so she was diligent about condom use. Beth had made it clear plenty of times that she didn't want to see that practice slipping away, and so she kept every bedroom stocked with them.
"What are you suggesting?" Tyler said.
Lilly felt him shift against her back. He was already getting excited. This made her lust flare up as well. She had been horny all day and was planning to get fucked tonight one way or another. At the same time, she was wary of where this was headed.
What Lilly didn't know was that, with the weight she put on at college, her birth control was no longer dosed correctly for her body mass. The days like this one, when she felt extraordinarily horny, just happened to fall halfway through her cycle, when she was most fertile.
"They need practice. I'm thinking we can do some time trials, to help them last longer and longer," Beth explained.
"Like...fucking? Right here?" Emily asked. Usually the coeds pared off into separate rooms.
"No, not fucking. Just getting them acclimated," Beth said. Then she added, "And it'd do the most good if each of the guys gets to try each of us. To the extent that we represent the breadth of the feminine form. What do you all think? Or we could just keep sitting around drinking, if you prefer."
"Count me in!" Mika said quickly.
"Sounds like fun to me," Emily said. She stroked Brian's arm, but he was sitting there stunned and quiet, maybe still sullen from being embarrassed in front of the group.
"I wouldn't turn down a chance like this," Tyler said, half to the room and half to Lilly in particular.
"Guys, I hate to burst your bubble, but there's one small problem with this round-robin idea," Lilly said. "Brian's my brother."
Beth turned to her. "And? Lilly, we knew that when we accepted him into the household. You know the house rules. Anyone can have sex with anyone else. We're all okay with it, if it happens. But if it helps at all, we're not talking about having intercourse here. Just contact." Then she asked Brian, "Are you in?"
