Aaron lay awake on the couch in the morning while he waited for Stephen to return. He stared blankly at the spinning ceiling fan as he ruminated over the activities of last night. He knew from high school that Kristy was a fun and attractive girl and he was attracted to her, but she was his stepsister now. He had told himself repeatedly that he could not act on his impulses since it would be considered wrong and could jeopardize his father's chances at happiness, but when the time came, he couldn't even hold out one single day. Not one single lousy day went by, and he was already in bed with her. What was wrong with him? He was relatively drunk at that point, but he still should have known better. He should have put a stop to everything once Kristy started touching him. Somehow, he couldn't control himself, there was something about her that drove him absolutely wild, even more so than when he knew her in high school, and he couldn't stop himself from letting things get out of hand.

Furthermore, there was the fact that Kristy obviously kept herself relatively chaste otherwise and yet was so willing to initiate their sexual activities almost immediately. The comments she made led him to a theory that he shuddered to think about.

Aaron heard the door unlock, and closed his eyes while pretending to sleep as Stephen walked in. As Stephen entered, Aaron feigned to yawn and pretended to wake up.

"Hey man, what's up?" Stephen asked.

"Hey, hope you had fun last night," Aaron responded.

"Sure did. So, how about you, you get any action last night?"

He almost instinctively said yes, and then realized that would be a terrible idea.

"Oh, uh, no, no I didn't. I didn't want to leave Kristy alone to fend for herself; there were some belligerent drunks there and I didn't want to leave her unprotected."

"Oh, right, good call! Shit, I'm sorry, I didn't even think about that. Well, thanks for taking one for the team, the next time the three of us go out I'll stay with her so you can get some action."

Aaron laughed and thanked him as Stephen went to his room.

After the events of last night and the comments she made, Aaron knew he had to confront the possibility of a horrifying theory. He reluctantly began to consider if Kristy's instant eagerness to take him to bed had something to do with some sort of desire she secretly harbored for Stephen, and she used Aaron to take his place now that he was technically her brother as well. It certainly made sense, the comment about "keeping it tight" for him, calling him brother all the time, and being so casual with Stephen when they were out. The thought of her harboring those desires made him squeamish, but then he felt bile start to rise in his throat as he began to wonder if the two had ever sexually experimented before. He didn't think it was likely, as Stephen seemed to be disgusted whenever Kristy would be flirty, wear provocative clothing, or talk about sex, leading Aaron to think it must be a one way deal.

Later in the afternoon, Kristy left to go to summer class and Stephen went to a job interview (which made Aaron remember he needed to look for jobs too). Aaron had to get some sort of answers about his suspicions, and there was only one way to do that. He walked back up to her room and opened up her laptop. He hated sneaking around and invading her privacy, but he had to know the answer or else the possibilities would destroy his mind.

It prompted a password for unlock. Aaron had a good idea what the password was.

He entered the word:

S-t-e-p-h-e-n.

Didn't work. He thought of something else.

B-r-o-t-h-e-r.

Bingo. Access granted. Aaron thought that should probably be proof enough there, but he decided to check her internet history to see if there was any clues. He looked down the screen.

"Let's see...Google, YouTube, fashion tips...." he mused out loud as he scrolled.

Then he saw it. A search for "brother/sister Incest stories." He felt like there was a dagger through his heart. Kristy had searched for terms like that and similar terms, resulting in a series of erotic stories and porn videos containing those things. These searches went back to a time period well before their parents had started dating.

Aaron closed the laptop, put it back in its place, and sighed. He had almost undeniable proof that the reason Kristy was so eager to take him to bed within the first day of knowing each other as stepsiblings had little to do with him and more to do with her expressing her feelings towards Stephen. He had thought they had shared something special, but she was only using him as a stand-in for her repressed incestuous desires. He was dealing with someone who had severe issues, and he had taken advantage of her.

Aaron went downstairs and paced around the house, contemplating the situation. His initial feelings of guilt and pity slowly turned towards rage. He felt cheated that she used him as a stand-in for Stephen. He was a star in college; girls at Pitt always told him that before they slept with him they would fantasize about him when they were with other partners. Girls weren't supposed to fantasize about other people when Aaron was making love to them -- and they sure weren't supposed to use him to fantasize about their own damn brother!

Aaron resolved never to sleep with her again, no matter how electric and pure their lovemaking felt.

Still, he thought, couldn't deny their chemistry, and he began to think back to the previous night and how wonderful it felt. He couldn't stop thinking about how amazing she felt as he was inside her.

Aaron started to reconsider his position. What if he was doing her a good service? Her unrequited feelings towards Stephen were totally wrong, and maybe as a non-biologically related stepbrother he could help her get over them. Over the course of the next few hours, he got over his guilt, jealousy, and rage and resolved that this was the right course of action. He figured that he was actually helping her out with her emotional issues and doing a good service. There was nothing technically wrong with the two of them having sex, and why would Aaron turn down an opportunity to be altruistic while at the same time sleeping with a girl that he was crazy for?

Later on in the day, Stephen walked in to the house with a beaming smile.

"You look pretty happy," Aaron laughed. "I take it the job interview went well?"

"Oh, more than well," Stephen replied. "You're looking at the newest Accounting Clerk at Van Tessler Industries, Phoenix Division!"

"Wow, congrats! I'd say this calls for a shot, what do you say?"

"Well, I'm not much of a drinker, but I do make exceptions for special occasions, and I'd say this is one!" Stephen laughed.

Aaron walked over the cabinet and pulled out some whiskey, pouring each of them a shot, and then went to the fridge to grab a Pepsi for both of them as a chaser.

Aaron was genuinely excited for the news. Foremost, he was happy for Stephen, but now in the back of his mind he knew that he was happier about the fact that Stephen would be out of the house for most of the day and Kristy and Aaron could have the house to themselves.

Aaron eventually poured another two shots after that, and the two of them began to bond while talking about their lives growing up. Aaron started by talking about being raised by a single father, how his dad got him into football, and other topics.

Stephen explained his life growing up as well. His parents divorced when he was two years old, right after Kristy had been born, and apparently it was a nasty divorce. His father, Allen, had accused his mother of cheating on him and there was a long and drawn out legal battle over money and the custody of the children. Eventually, they settled on the plan that Stephen would live with their father and Kristy would live with their mother. As a result, Kristy and Stephen almost never saw each other while growing up, as the divorce was so bitter the two of them didn't see each other often and weren't raised together. Once Stephen was ready to enter high school, however, his father got a job offer in New York and Stephen opted to stay in Arizona while living with his mother and sister despite the fact that he hadn't interacted with them much.

This explained a lot in Aaron's mind -- he vaguely recalled seeing something on the Discovery Channel one time that being raised together is how a person recognizes someone else as a sibling and not a viable sexual partner. If Kristy was raised separately from Stephen, she doesn't have that taboo filter turned on. Whereas Stephen probably has some memory of her being born and her being a baby so he still thinks of her as a sister. While Stephen was talking, he did some Google searching on his phone and found that this theory is called the "Westermarck Effect."

An hour later, Kristy came back from class and found out the news as well. The three of them drank to celebrate Stephen's new job. Aaron watched their interaction together closely, but nothing seemed amiss. Stephen told them that tomorrow he would fly out to Los Angeles on the company dime for some training at company headquarters and would have to stay there for a couple of days. Aaron was delighted at this news as it meant that he and Kristy would have the house to themselves for that duration.

Still, however, there was the issue of what to do tonight while Stephen was still there. Aaron considered that he should refrain from sex for this one night, but watching Kristy's body as she drank and leaned against the kitchen countertop left him with little choice. Aaron wanted to use the alcohol to make sure Stephen was fully passed out so he and Kristy could continue their adventures that night. Aaron knew that Stephen wasn't much of a drinker except on special occasions, so he decided that with his higher alcohol tolerance he could attempt to get Stephen to try to keep up with Aaron and then pass out. Aaron kind of felt bad about doing this but he knew it was for the best, as Stephen would most certainly not want to hear his sister fucking their stepbrother and it would involve him in a mess of complications. Also, Aaron thought, as someone who only drank on certain occasions it didn't hurt for Stephen to cut loose once in a while.

What's more, Stephen was a very humorous drink. "Hey....you guys....listen...." Stephen drunkenly stammered later in the night as the other two laughed, "I just....so good...now I'll push some pencils....get some of that MOOLAH....good...good times. Hey Aaron man thanks.....thanks BRO....good to have a brother now..."

"Same to you man, appreciate it," Aaron responded. He felt a little guilty for getting him drunk now.

"And with that I'll....I should probably....hit the hay and shit." Stephen drunkenly stammered into his room and plopped onto his bed. He was out cold, and the way he was positioned caused him to start snoring. Aaron laughed and went in to turn off his light and close the door for him. Aaron walked back to the kitchen, where Kristy was leaning against the counter and started writhing her hips against it while looking at Aaron with "fuck me" eyes.

He walked up to her and grabbed her hand. "If it wasn't so risky, I would want you to fuck me right here on the counter top," she whispered to him.

"We'll save that for tomorrow...you know, when we have the house to ourselves," Aaron replied as he kissed her on the forehead, and the two of them walked upstairs to her bedroom.

Once they were in the bedroom and shut the door behind them, Kristy put on some music quietly from her iPhone and started to shake her ass in her tight jeans as he took off her shirt, doing a striptease for Aaron as he sat on the bed.

"Hey listen, before we start..." Aaron told her as she started to undo her bra.

"Yeah?" she replied.

"I really think you should cut out all that calling me brother and saying you're my sister stuff. It's kind of weird, I don't think of you as a sister."

She laughed and walked over to him, putting her finger on his mouth as her bra fell off, exposing her perky yet large breasts. "You're a lying liar. Whenever I called you big brother you started pumping me faster and more vigorously!"

Aaron thought to himself "I was going faster because I needed more stimulus since the incest stuff is a turn-off!" but decided against saying it aloud.

"You love it. You love having a little sister who's a slut for you, that you can fuck whenever you want," she said as she slowly moved her jeans and panties down her legs and walked over to him for a night of passion. "So, how do you want me tonight, big brother?"

----------------------------------------------------------------

Aaron made love to Kristy as much as possible in the next few days that Stephen was gone, taking advantage of the fact that they had the house to themselves to have sex in any location they pleased.

On Saturday, they decided to go clubbing. Since no one there knew they were stepsiblings, the two of them openly got grinded in a hot and heavy manner on the dance floor while occasionally making out.

"You dirty pervert," Kristy laughed at one point after she removed her lips from his, "you could have any of the girls at this club, but you choose to go home with your own sibling."

"Hey, the same goes for you, vice versa!" Aaron replied.

"Oh, it's a no brainer for me. Have you seen the other guys here? All losers compared to you. I roped the big prize. All these other women in the bar know it, they've been looking at me with daggers in their eyes all night." After spending so many months in a state of mild depression after having his NFL dreams crushed, he loved how Kristy would help his ego like this. More importantly, he could tell it wasn't just empty words of flattery and that she meant all of it.

Kristy went to the bar to go get some drinks. When she was there, a stunning woman with flowing golden blonde hair approached him. She was thin, about 5'7 but with a decently round waist, wearing a low cut top in a blue dress that showed off her ample breasts. She seemed to be a few years older than him.

"Excuse me," the woman asked, "are you....Aaron Sanders?"

"Why yes, yes I am. Do you know me from somewhere, or are you a big college football fan?"

"It's the latter. I went to Cincinnati, so I saw you play us a few times. I also watched a bunch of your other games."

"Well then, you obviously have a pretty good memory to recognize me by face. I had my helmet on most of the time in those games!"

"Well, actually," she chuckled flirtatiously, "I went out of my way to watch as many of your post-game interviews that I could , since I thought you were cute."

Aaron continued flirting with this woman, who he found out was named Tracy, and felt somewhat of a connection with her. In the back of his mind, however, he was nervous, as he wasn't sure how Kristy would respond. Was he prevented from having sex with other girls now? Was he in a serious relationship? What had he gotten himself into?

He saw Kristy walk back towards them. When she saw him talking to Tracy, Aaron dreaded her reaction, but he was then delighted by her response. Rather than look disappointed that he was talking to someone else, her eyes lit up. She gave him a thumbs up, then held up three fingers to represent the number "three," and then made a cute pelvic thrust motion. Aaron laughed to himself, as she was obviously giving him a hint that she was willing to engage in a threesome. Aaron had participated in a few threesomes in college and had found them quite satisfying, so he certainly wasn't turning that down that opportunity.

Aaron asked Tracy if she wanted to dance, and she agreed. They exchanged numbers as he began to grind with her on the dance floor. During breaks from dancing, he continued to talk with her for a bit and saw that she was a fun and interesting person. After twenty minutes or so, Tracy left to go to the bathroom for a bit, saying she would be back in a few. Kristy, who had been watching the whole time, walked up to Aaron while smiling.

"This is great," she purred, "let's take her home and the three of us can have some fun."

"Sounds like a plan, but you have to pretend to be my girlfriend, of course. Absolutely no mention of me being your brother or you being my sister...for real this time."

"Well, duh!" she laughed. "We can't have anyone finding out what big perverts we are."

Tracy returned from the bathroom and saw the two of them talking.

"Oh, hello," she said to Kristy apprehensively, "and you are?"

Kristy stuck out her hand to shake Tracy's. "Oh, hello there. I'm Kristy, Aaron's girlfriend."

Tracy took...