Not Really Worth The Wait

My wifes sister and have always had a little sexual chemistry between us from the first time we met almost 30 years ago. Since forever, a few stray comments, some very low key flirting here and there, more when no one else was around. She's always known she makes me hard and I know I've made her wet. Not a secret to either of us since when we've teased each other when we were alone, we've admitted that to each other but always agreed we couldn't do that to our respective spouses. Just teasing and each enjoying that. Until last Saturday.
Her husband, my wife and a bunch of other people went on a 2 day snowmobile adventure. I had knee surgery a couple months ago and not ready for that yet. She just hates snow and cold. Saturday afternoon, we're hanging out and yep, heavy flirting and teasing like usual and I told her, jokingly, "careful, you're looking too good in that skirt, I might not be able to stop myself"

We were sitting on the couch. She stood up, walked in front of me and lifted her skirt up to her waist. No panties and very neatly trimmed with a tiny landing strip and just beautiful. I looked up at her, she down and me and said, " one time, no one ever has to know"
Throbbing hard at this point, I lunged at it as she moved onto the couch and straddled my face. She smelled amazing, very wet already and tasted incredible. Ate her to 2 substantial o's til she moved off and turned to reach for pants that were quickly off and my cock in her mouth. She was very vocal when I was eating her out and vocal and dirty talking while slurping and actually gagging herself on my cock. I stopped her so I would cum too fast and took her to the bedroom. On the edge of the bed, still talking dirty and I'm loving it. Legs up and she said, don't be gentle. Ok, lined up and literally slammed into her hard. She went quiet. Asked if she was ok, she said yes, so went back to it.
Here's the problem, from that moment, not one more sound, like none. Eyes wide staring at me, no expression at all. Just total zombie. 30 years of build up, her telling me a little while ago how much thicker my cock head was than any shed ever seen, being dirty and eager, to nothing. Not even heavy breathing while I'm pounding her hard. Just a dead lay. I was trying but couldnt cum. I had to put her in doggie and literally close my eyes and think of my wife before I could cum. And I did, a lot.
She moved forward pulling herself off my cock, cum dripping off me and out of her and that's when she made her first sound. A great big uhhhh and said " you seriously have the biggest cock I've ever had in my life. That was the hardest, fuck I've ever had. You stretched me hard, lol"
Huh?? I know she wasn't lying cause she really was tight, tightest I've had since high school and way tighter than my wife for that matter but, wtf? She's just a cold fish on her back, apparently.
I'd definately exchange oral with her again if the opportunity presented but, I couldn't fuck her again. Not into an inanimate fuck doll. I like the interaction.