My friend and I are both married, my wife and I are very close with he and his wife. As couples we have done a lot together, with very few secrets between us. We have skinny dipped a lot with them at their house, and have become very comfortable being naked around each other, even a little touching of each others spouse wouldn't even raise an eyebrow. We have even gone as far as having sex in the same bed together. Never fully swapped, the farthest we would go is massaging.
As we started having children, things started to change with our wives. They didn't want to do much of anything anymore, not even skinny dip. When this became more frequent, I started to see changes in my friend too.
My wife and I went to our friends house for dinner, and wine tasting. We decided in advance we would spend the night rather than drive home, knowing it would be a late night, not to mention safer after all the wine. After all the wine tasting, and the other guest left, my friend said to me, "the water is warm", code for the hot tub is ready. I said, sounds good. I told my wife, grabbed my wine, and headed for the backyard with my friend, knowing our wives would follow. We got to the hot tub, and started to take off our clothes, as our wives arrived. I asked the girls if they were going to join us, and one after the other, said, "no". All the pleading in the world wasn't going to change their mind, so we just accepted it.
We continued undressing in front of them, and stepped into the hot tub. A few minutes later my friends wife started yawning, and said, she was going to bed, my wife did the same a min or two later.
So there we were, naked and alone talking about the good old days when the girls were eager and willing to join us, and just missing the fun naked times together. Of course being guys we were being very sexually explicit, in our conversation.
Then my friend started telling me how the conversation was turning him on.
I just sort of laughed it off, and said, yeah, too bad the girls aren't here now.
Then he was telling me how he has gotten himself off with the jets in the hot tub before, by putting the head of his cock up to the jet, and moving it back and forth in front of the stream. As he was explaining, I could see he was doing it at the same time. He told me to give it a try. I resisted at first, but he kept egging me on.