So I suppose I should start with a little bit of backstory. My name is Jason, I'm 35 and happily married to my wife Kate who is also 35, we met as freshman in college and stuck together ever since.

Kate has a sister named Madison, she is 10 years younger than my wife, we spent quite a bit of time together over the years, I did my best to ignore that Madison was growing into a beautiful young woman, but noticing was unavoidable.

Madison is lesbian, and moved into an apartment down the hall from us with her long time girlfriend Ash. It isn't unusual for the 4 of us to get together to drink a bit and watch some movies on the weekends.

I always got on great with Madison, she generally didn't care for men but always told me I was an exception.

I'll fast forward to that fateful Sunday morning where Madison and Ash popped a question on my wife and I that made our head spin.

They wanted to have a baby, which we thought was great news, my wife exclaimed her happiness at the thought of a little niece or nephew. Then Madison interrupted with, but we want Jason to be the donor.

My wife said she was okay with it, I joked that I could go to the clinic and do whatever she needed into the cup, which elicited a giggle from the room.

Ash says they can't afford a clinic, they had looked into it and it was entirely out of the budget. My wife interjects with a DIY insemination kit she found on Google. Madison shudders at the idea of some homemade turkey baster kit.

Madison says, "I don't really know much about guys but like, is it possible for you to... Y'know, shoot in me without us really having sex?"

I give her a puzzled look, glancing at my wife who looks equally confused. Madison continues looking at Kate saying, could you like get him "almost there" then he just finishes in me?

At this point my head is really spinning, is she really suggesting what I think she's suggesting? I look at my wife, judging her feelings on the situation.

Kate pipes up and says she thinks that would work, I now comforted by knowing that my wife is on board, chime in with a nervous "I think I can do that."

Madison announces that she's going to be at peak ovulation tonight and we discuss boundaries.

Kate says she will ensure that I'm "ready to go"

Ash says she will do the same for Madison ensuring she's warmed up and ready for entry.

Ash looks at me and says, remember she's not for your enjoyment, you do your job and get out.

I nod in agreement

Nighttime rolls around, I do my best to contain my excitement at the situation. I can't deny that I've been curious for many years what it would feel like to bury my cock in Madison.

I walk in and the girls are all in sexy lingerie with crotchless panties, Ash is using a clit suction toy on Madison, her moans already filling the room, driving blood into my growing erection.

Kate pulls my pants off and begins giving me her all with her top notch oral skills. I marvel at the sight on the bed, Ash is going down on Madison causing her hips to buck and her moans to get louder and louder.

I feel my balls start to tighten, I signal to Kate that my orgasm is pending, she stops, stands up and says "I think he's ready girls" in a cute sing-song voice.

I ask Madison which position she wants it in, she bends over with her ass in the air, I take this as my signal and spread her pussy lips apart with my cock. I push forward slipping in with ease, as Ash had done a wonderful job getting her "ready".

I slide in slowly until my entire cock is buried in her, every inch feeling better and better as my dreams of fucking her finally became reality. I stop to gather my senses for a moment, my thoughts are quickly interrupted by Ash saying "Did you do it?".

I grunt back no not yet, I'm really close though. Ash says "Well hurry up, I told you to do your job and get out". My wife in a teasing tone of voice says "yeah hurry up and cum in my little sister".

I tell them I need a few pumps but I can do it, I slide back out and pump into her, she moans in pleasure, I can feel my orgasm building up. I want to savor this moment and unbeknownst to everyone else in the room do my best to hold back, pumping faster and faster into Madison's pussy.

Ash says, "Just do it already!" In a more demanding tone, I pump faster and faster and let go, my cock buried deep in her, pumping stream after stream of seed into her. I grunt as I fill her.

In the haze of my orgasm I remained in her for a moment until the annoyed tone of Ash saying "Ok! You're done get out of my girlfriend, Now!"

Not wanting to cause any issues, I pull out, Ash leads Madison to the bathroom to clean up the "gross guy juices" off of her. Kate gave me a look and a smile, knowing deep down that I'd always been curious about her sister.

Once Madison and Ash left, Kate asks if I've got any left for her, and we had a night of great sex. I'm not gonna lie, I couldn't help but imagine it was Madison a few times.

The first "session" didn't work, after much teasing from Ash about my manhood and weak sperms we tried again, also failing. This lead to finding out that Madison was mostly infertile. After much debate between the two I ended up having a successful "session" with Ash. Those times are for a part 2 though.