Hot tub buddy

A friend of mine has a hot tub and invited me and my wife over for drinks and relaxing in it. I already was aware that they had the hots for each other, but I secretly wanted them to screw. I couldn't decide which idea was hotter, having them sneak off somewhere or a threesome. While in the tub sipping wine, I noticed he was playing "footsie" with my wife and she was trying not to smile about it. After a bit of this, he casually put his arm around her and dared us to go nude. She looked at him, straightened up and took her top off. We slipped our trunks off and our buddy had a very prominent hard-on! I was shocked when my wife reached over and gave it a playful tug--she was ready! He pulled her close and rubbed his prick on her lower abdomen; she looked over at me and I told her "You can't stop now!" He sat on the edge of the tub while my wife sucked on him, then they got up and went over to a padded bench where he mounted her and started fucking, slowly at first. When he got it all in, he began pumping harder, his wet balls made a "slap, slap" noise. She came again and again, and watching them was driving me wild. He bowed up and yelled "Oh, fuck!" as he shot his wad. I'd been waiting for that moment with my pecker in my hand! He pulled out and got out of the way for me. My dick slid in with no resistance, but I loved the feel of my wife's freshly-stretched pussy full of another man's cum. We still do this from time to time, and we have an agreement for my wife to go over there without me while I'm at work--as long as she tells me about it. We call it "paying for membership in the hot tub!"