All parties involved in this story are 18 and over at the time of the story.
I want to first thank everyone for their comments and assure you I will take them into consideration as I go forward.
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While I may have started fooling around with Alex first we never really had a good relationship as brother and sister. She was always just my little sister that I tolerated because we were family. Don't get me wrong she wasn't a bad looking girl just our personalities didn't get along with each other.
Now for our baby sister Bess we always got along in fact it was rare to see one without the other when we were home. Bess is 5' 4" with long blonde hair, baby blue eyes, curves in all the right places, and 32D breast. In fact even before I had started fucking Alex and decided there wasn't anything wrong with fucking family I found I sometimes got an erection thinking about Bess. Bess always hung around with me no matter what I was doing when we were growing up which made her a bit of a tomboy but she always had my back.
So it was no surprise to find us wrestling around one afternoon in my bedroom when things took an unexpected turn in our relationship. The thing you need to understand is that even though I had been fucking Alex for awhile it had never occurred to me to try anything with Bess. Bess was my buddy my partner in crime the one I knew exactly where I stood with her and wasn't willing to risk our bond just to fuck even though I wanted to since the first time with Alex.
I reached to grab a hold of Bess so I could pick her up and body slam her when my hand slipped. Now we had been rough housing for awhile and we both were covered in layer of sweat. So that when my hand slipped it went right down her shorts into her panties and I got my first feel of her mound. I quickly dropped her on her feet pulling my hand out after getting a nice feel of Bess and then stepped back away from her.
That is when Bess gives me this shocked look and ask me "What do you think you are doing Joe? You shouldn't be touching your little sister like that or there!"
I answer her saying "It was an accident I would never do that to you on purpose Bess! I would never try to take advantage of you in any especially in a sexual nature." That is when I got the surprise of my life when Bess reached out and grabbed me without any warning.
I was startled and jumped asking her "Bess what do you think you are doing? It is just as wrong for you to touch me as it is for me to touch you."
To which she calmly responded "Just making us even Joe what is that not ok with you? Shouldn't I at least get to grab you just like you already did me?" It was only at this point did the idea of fucking Bess even enter my mind and as soon as it had it came with an incredible urge to make it happen.
So barely missing a beat I say "Weellll it isn't quite the same since my hand actually went down inside your pants and panties" trying to see how she would react. I figured depending on how she reacted I would know if it was possible to start something with her. Little did I know what exactly I was about to get myself into or what would become of us afterwards.
Bess cracks a grin and says "Like you would let me put my hand in your pants and grab your dick on purpose so I took what I could get by with." That is when I decided to see how far I could take things before she would get scared or think about it too much.
So I shut and locked my door then went back over to her and dropped my pants saying "Well it is only fair since I grabbed you and you should get to grab me with full contact." This really did surprise but I got to give her credit she recovered quickly.
It took her a few minutes of sitting there staring at my cock before she said "Are you serious or what? You can't seriously be offering to allow me to grab your cock just to make us even."
I simply said "Hey I am only trying to make us completely even but if you don't want to it is your choice it doesn't matter to me. But then again I guess if we are to go for a complete balance I should get to grab you through your pants but again only if you are interested in us being equal." This whole time she has not stopped staring at my now erect cock.