So this happens a few years back. It involves my wife's best friend. Well call her Christi (30F) at the time wife (30F) and me (34M) . The 3 of us when to a camp site that had a lazy river, that you could rent inner tubes and relaxed as they river circled around the park and some wooded areas.
This day not a lot of people where there, and even less people on the river. So my wife and Christy are in their bathing suits and I'm in swim trunks. Me and Christi have always flirted with each other but nothing that ever crossed the line.

The flirting would consist of her say things like your trying to get your wife wet wearing that shirt aren't you. Or me telling her if your going to wear that don't walk in front of me. My wife would always laugh and her own comments.

Well that day when I saw her in her swim suit I told my wife keep your girl away from. I need to keep focus on the water. Christi says don't worry we'll see if the print grows. My wife says don't worry the water should be cold enough and laughs.

Well we are on the river for about 30 minutes when we get to a really quite are under a wooden bridge .my wife says she wants to take a picture there. So we get out of the water and get our phones out and take a few pictures. But the phone back in the bags and Christy slipped trying get back on her inner tube . I go to help her and her thigh made contact with my croch . instant hard on. The. I slipp and go underwater I go to sand back up and I must have pulled Christy down with me. So now I am face up under water and Christi is on top of me . I try to get up but now she is sitting on my hard cock . But my swim shorts are holding in .. she stand up and so do I. My wife comes behind me and pulls me up . As she does I feel my shorts start to slide down. My wife is behind me and Christi is infront of me asked me if I was ok. I say yes and ask if she is ok. She says yes then tell my wife I your hubby got hard. I then feel my wife's hand on my dick. And my shorts pulled down . At this point Christi has turned her back to me. And my wife just pushed me to her . My hands go around her waist . She leaned forwarded onto her inner tube and I really was not trying and still don't know how it went in. But my did just slides right into her. She lets out a moan and my wife comes behind me and ask me are you inside her ?.

I said it just slide in I wasn't trying to do it. She said well your in her might as well finish . The rush and excitement off it caused me to cum in like 10 strokes ..But we when be got back home we did go for round 2 three and 4. As my wife watched and commented ..