I intend on this being a series so with that in mind this first part is a little slow for those wanting knock down drag out sex.  This is basically the back-story of how things started.  I’ll admit that some of this is very real, some of it may be a bit of a stretch of the truth and other things potentially just fantasy.  It’s up to you to decide what’s what if it matters, but just know that this is an ongoing thing and not every ‘story’ is going to be all about the sex.  Anyway, this is my first attempt at anything like this so please be kind, enjoy and leave comments as to what you like or don’t like.  Thanks.
My name is Robbie Bartlett.  I’m 42 years old.  Jenny - my wife - is 39 years old.  We‘ve been married for nearly 20 long years.  I suppose can consider it ’long’ when you get married at 22 and 19 and thought it would be forever… sometimes you just might get what you wish for.  
I could have left, I’m sure that’s the first question or thought that came to mind when interpreted that I’m not happy, which of course I am not.  However, I am a father to 2 very lovely young ladies; 18 and 17 now respectively.  And I made a promise very early on, both to myself and to them - even though they would not have understood - that no matter what I would always be there, and to me that actually meant and still means BEING there.  Divorce was never an option.  My own happiness would be sacrificed to make sure that I was actually a dad to them and not just someone that saw them now and then.  Please don’t think that’s an attack on anyone that’s had this situation happen to them and sought a way out, we all have decisions to make in our lives and have to live with the consequences of those decisions.  It’s just what I personally decided to do… and I’ve had to live with that decision.
Of course it’s not been easy.  
Although I suppose in all honestly it always hasn’t been that bad.  The first few years were rough because we were young and struggling with our careers and didn’t have a lot of money or really free time to do much besides just work and fight, and we did a lot of fighting early in our marriage.  Unfortunately as we grew up we stopped fighting as much because we just sort of stopped communicating in most matters.  We grew apart.  This made the marriage ‘better’ in that there wasn’t constant attacks coming from all sides and we just sort of did our own thing, but obviously that’s not the definition of what most people want from their marriage.
We still ‘pretended’ or at least acted out that things were mostly civil.  Of course friends and family knew that things weren’t good, but as long as we still went to family events together, did things with our children together at times and didn’t try to kill each other they mostly just left us alone and probably just figured it was our lives.  So that’s what we did.  We typically presented a unified front and still tried to hold the family together inasmuch as we’d go shopping together, to the zoo, take the girls out to the movies, dinner… all the normal things that most normal families do.  But then behind doors, we pretty much just ‘lived’ with each other while completely living apart.
Unfortunately that created other complications.  I was still a man.  She was still a woman, although her sex drive wasn’t nearly what mine was, and in fact she’d even admit not what most women’s were either.  Truth is she really didn’t need sex.  She had only been with a couple of guys before me and neither of them - by her account - were all that good.  In fact the first time she had sex she had basically been raped by her boyfriend - although she says she ended up giving in and going along with it - she hadn’t wanted it at the time.  The second time she slept with his best friend to get back at him for what he had done.  Beyond that, there was nobody else.  I was the first guy to give her an orgasm and whenever we did it she seemed or at least said she enjoyed it, but it was always hard to tell with her, especially since she never really wanted it.
I suppose it sounds a bit cliché and maybe even a bit harsh that the wife didn’t want it so I started looking elsewhere as if sex was the one and only most important thing in our relationship or any relationship.  But that’s not really the case.  Sex was just one of the reasons.  And honestly I didn’t really set out looking for other relationships or partners or anything.  Yes, I certainly was a flirt and did a lot of looking and dreaming and fantasizing.  If you didn’t know most guys do that whether happy or not - but that’s all it ever was.  For the first 4 years of our marriage I was mostly faithful.
I say mostly because I would imagine some people consider flirting and fantasizing as being ‘unfaithful’ to some degree and I’m not here to argue semantics.  Let’s just say that I didn’t have sex or sexual contact with any other women other than my wife about once or twice a month if I was lucky.  I lived mostly on porn and fantasies.  And my biggest fantasy at the time was her sister.
Yes, her sister.  Her sister that for the first 4 years of our marriage I hadn’t even met.  See we lived in the Midwest and her sister lived with her parents in southern California.  Of course I had seen pictures and as gorgeous as my wife was - and she was gorgeous with her long flowing dark hair, big round brown eyes, large pouty lips and huge natural 38D’s - her sister was even more so.
 Elizabeth, since she had pretty much turned 14, was already just about a full-grown woman.  She had long black hair, gorgeous deep brown eyes, perfect lips, 36D on top with a slimmer waist than her sister and at only about 5’2” compared to Jenny at 5’6” was a tight little package.  She was the definition of sex.  But it was more than that… she was a flirt.  And it seemed her favorite target was me.  Even though we were halfway across the country from each other and I was married to her sister - or maybe because I was married to her as I found out later on (but that’s another story) - she really just seemed to enjoy making me as hot and horny as she could when we talked on the phone… and we probably talked on the phone more than her and Jenny did.
The funny thing was that Elizabeth was a virgin, but the stories she told about her boyfriends and how far she’d let them go - while pretending to ask me questions and get my advice on things…… let’s just say ‘damn’.  She’d constantly talk about the things she wanted to do, but hadn’t yet, and how she’d be as a wife - knowing FULL well that Jenny was exactly the opposite.  Whereas Jenny was quiet and reserved and didn’t much like sex, Elizabeth was wild and free and constantly talked about how she’d fuck her husband every night, let him do whatever he wanted to do to her, let him be with other women if she could watch, how she’d sleep with another woman if he wanted her to….
She was good.  And it was really starting to piss Jenny off, because she knew how much it was turning me on.
Anyway this flirting and teasing had gone on for pretty much the last couple of years, ever since Elizabeth had turned 15 and really started to mature.  She was 17 now and her family was moving back to the Midwest - just a couple of hours away from where Jenny and I lived - so she called us up and gave us the news that she was going to come for a visit on the way to their new place.
I was ecstatic to finally meet her in person and my wife was honestly happy that she was going to get to see her sister again, who she hadn’t seen for 5 years now since she moved out here.  Don’t get me wrong, there was nothing devious about my intentions at this time.  It’s not like I was already planning on how I was going to get her in bed or anything like that.  The teasing and the flirting was fun and I expected she’d do her best to turn me red when she saw me and probably know full well I was masturbating in the middle of the night thinking about her, but other than that, I didn’t expect or dream of anything else ‘real’ happening.
Anyway another month passed and before long it was the middle of July and the weekend she was coming to visit.  I got up that morning with probably the biggest smile I’ve had on my face since the birth of my girls.  I had a very hard time trying to convince my wife that it was a normal day although I don’t really think that she thought that anything would happen either and in fact Elizabeth and I hadn’t even really flirted all that much since she said she was coming up so Jenny hadn’t really said much either.
When the doorbell rang I held myself back and let Jenny answer it - although I was standing at the top of the stairs to get my first look.  Yep, she was every bit as gorgeous if not even more so in person.  The last picture I had seen of her didn’t even really do her justice.  She had cut her hair a bit shorter so that it just fell off her shoulders now but other than that, she was nearly the perfect little package.  She had on a very tight low-cut blouse that really should have been illegal with as much cleavage as she was showing and tight cut-off shorts that shaped her heart-shaped ass just fine.  I think I may have been sweating at this point.
She hugged her sister and then looked up the stairs to me.  “Who’s this handsome guy?  Did you kick Robbie out?” she smiled, before literally bounding up the stairs and into my arms, giving me a very tight hug, which pressed her tits right against my chest and placed a soft kiss on my lips.  “Nice to finally meet you in person.”
Now I know I was sweating and couldn’t even respond for a second while I caught my breath and wondered if Jenny was going to stab either her or me in the back for that kiss.  “Nice to meet you to, sis,” I finally whispered.
“So where am I sleeping?” she asked coyly and with a smile again on her incredible lips.
With me of course, was absolutely the first thought that passed through my head, but a glimpse of Jenny walking up the stairs behind her put that out quickly.  “We prepared the spare bedroom, it’s down the hall from our room.  I’ll get your stuff.”  And with that I moved past Elizabeth before anymore harm could be done here and went to the car to grab her things.
The first weekend was pretty uneventful - and I say first weekend because that’s all she originally had planned on staying, as she needed to get to her new house and get things set up for the coming school year.  But Jenny convinced her to stay for the week and Elizabeth quickly accepted the invitation.  We honestly didn’t even really flirt all that much, at least not openly.  There were glances and smiles and I’d catch her looking me over and sometimes a quick wink, but it was really harmless I kept telling myself.  In fact throughout the week there really wasn’t much more than some innuendoes thrown around and some very harmless teasing.  Even Jenny seemed to be perfectly okay with how we were messing with each other and was much more comfortable than she usually was when Elizabeth and I were on the phone.
Then it happened.
It was Saturday morning, the day that Elizabeth was supposed to leave.  It was around 8 in the morning.  I had been up a bit late that night so was sort of sleeping in although I really wasn’t completely asleep.  I had been pretty restless that night and really hadn’t got a great deal of sleep so I was just sort of relaxing.  I knew my wife was up and assumed she was making breakfast or talking to Elizabeth before she was heading out that afternoon.
Elizabeth.  My thoughts turned completely to her as they had for most of the week.  That smile.  Those lips.  That body.  Those tits.  That ass.  It wasn’t long before my hand found it’s way around my cock and slowly started stroking it.  My eyes were closed and all I could see was her face.  That’s when I heard the door open slowly and someone walk in.  I’m not really sure how to describe the state I was in, although I’d imagine some of you have been there before.  I wasn’t sleeping - but I wasn’t awake.  I was conscious of what I was doing, but at the same time not really completely in control.  I slowly opened one eye just enough to peek at who had come in, FULLY expecting that it was obviously going to be my wife and I couldn’t have cared less if she caught me doing that at this time.
It was Elizabeth.  She had walked in the room and slowly closed the door behind her and was now standing at the side of my bed.  Let me be clear.  It was very obvious what I was doing.  Granted I still had the sheets up over my body, well they were at least covering the bottom portion and I was shirtless, but there would have been zero doubt that I was full on masturbating, stroking my cock from bottom to top, underneath the sheets.  And she stood there staring at me, with a smile on her face.
So I did what any guy would do.  I kept my eyes closed and I continued what I was doing.
And she just continued standing there watching me.
So I started to stroke it a little faster and gave out a very slight moan, tilting my head back a bit so that I could get a little better look at her though my partially opened eye.  She was starting to touch her breasts through her shirt.  Rubbing them, squeezing them, looking down at me.  I started to stroke it even faster then and that’s when she reached down and slowly pulled the covers off of me so that she could see everything.  I was definitely going to lose it.  I had no idea what she had planned but I wasn’t stopping now.  She walked over to the door and locked it.  I didn’t even think twice about it or what sort of an explanation we’d give Jenny should she have decided then that she needed to come back and check on us or if she was even home in the first place.  All I cared about, all I saw was this absolutely stunning 17 year old girl standing next to me, rubbing her tits through her shirt, watching me jack off.
I stroked it faster and let out another moan, but this time also whispered her name as well.  She definitely heard me as she now lifted up her shirt and let her breasts fall out and started rubbing them again, twisting at her nipples as she did.  “Stroke it, Robbie” she said.  “Stroke it for me, play with that cock, think about me.”
This wasn’t a problem.  It was even less a problem when she let go of one breast and moved her hand down over my stomach and touched me softly and then let it wander down and over the tip of my cock as I was stroking it.  “Oh baby, imagine you’re fucking me.  Imagine you’re putting that big cock into my wet pussy.  I want it so bad.”  She said softly and then leaned over and kissed my chest with her lips, teasing my nipple with her tongue.
“Lizzy,” came my wife’s voice from down the hall, “are you getting him up?”
“Oh yes, sis, I’m getting him up alright” she said loudly, “and off” a little more quietly.  “Cum on my tits, Robbie.  Mark me.  Put it on me so that I can walk back to the kitchen with your cream on me and my sister will never know.  Give me what I want before she comes down here and catches us, or hell let her catch us so she knows I can take whatever she has.”  
That pretty much did it.  I called out her name again and the first shot hit her square in her chest with the next blasting against her left nipple and then yet another doing the same.  She leaned down and took her tongue and ran it across the tip of my cock slowly before pulling back away.  “Thank you baby” was all she said as she put her shirt back on, not wiping the cum from her chest, not looking at me and walked out the door.
I laid there.  Did that really just happen or was I dreaming?  Should I get up?  I was both in shock and in complete disbelief - beyond being the most excited I had ever been in my life.  So I just laid there until I heard my wife scream for me that breakfast was ready.  I got up, cleaned myself off and walked out to the dining room where Jenny and Elizabeth and my 2 girls were already sitting at the table eating some eggs and waffles.
Elizabeth looked up at me and said coyly, “Are you feeling better?”
“Huh?” I stammered back.
“Well I know you weren’t feeling all that well last night so I just wondered if today had started better for you?”
I coughed, audibly.  “Yes.  Much better.  Much.”
“Good.”
I looked at her and at her nipples poking through her shirt and noticed a couple of stains and smiled.
She didn’t say much else to me for the rest of that morning, mostly just chatting with her sister about things that I didn’t much pay attention to, lost in my own little world at that point.  When it was time to say goodbye she gave me a very long hug, making sure her breasts were pushed against me as tight as she could and whispered in my ear.  “I hope that happens again or maybe even more.”  And then she turned, got in her car and drove away.