I could probably go on for a very long time about how this all happened, but I'll just try to give the main details.

I've been married to my wife, Kristin, for 10 years. We've got 3 kids together. Our sex life used to be great, but it's gone downhill. The last few years, it's been shit. We used to be spontaneous, have fun, and fuck. Now for her everything has to be perfect and planned and it just never happens. I've been very frustrated.

My wife's sister, Stacy, is 25. She's going through a divorce and has been living with us for about 2 months. She's also 29 weeks pregnant. Nice, round belly at this point. She looks a lot like my wife in the face, but younger. They've normally got similar bodies as well, although I think my wife's ass is a bit bigger, lol. Anyway right now Stacy is very pregnant, and looks great that way.

For the last month or so, Stacy and I have been fucking. We had always been flirty over the years in a friendly, wouldn't-dare-touch sort of a way. That continued here, up until that Saturday. My wife had the kids out at a birthday party so it was just Stacy and me at the house. We were talking, she caught me staring and checking her out. I apologized and she told me it was okay, that she was more than a little sexually frustrated herself. Somehow we wound up with her topless in the kitchen, wearing only some pink cotton panties that her ass cheeks hung out of. She gave me a blowjob, and then I very aggressively fucked her right on the kitchen floor.

We've been fucking ever since. Mostly random quickies and blowjobs. We don't have a lot a time and or privacy with everyone here. The sex is great. We don't really talk about it, besides random sexting. We haven't discussed how long this may last, or if it ends when she has her baby or what.