I can't really identify why the thought of sharing my wife (currently my ex-wife) turned me on, it just did. I ended up sharing, or letting her fuck alone, a friend of mine several times in our late 20's. Here's the first time. All true.
After a night out, obviously drinking, my friend Dan ended up crashing at our apartment. My wife was shitfaced and I was horny like I always am when she's shitfaced. She talks more dirty, she fucks better, etc. She didn't seem to care that I was taking off all of her clothes with Dan in the same room. He was sleeping on the floor next to our bed. She kept teasing him with lines like, "Dan he's taking off my clothes" and "Dan he's eating me". At one point she got up, naked, and walked to the door to shut off the light and he watched her.
On the way back to the bed she took his hand and dragged him onto the bed, which kind of surprised me. We had talked dirty about doing stuff like this but I didn't think we'd ever actually do it. Didn't matter, it turned me on like never before.
Once in bed I went back to playing with her, mostly eating her. At one point, and I'm not sure who started it, my wife and Dan started kissing. Listening to her moan and kiss another man while my tongue was in her pussy was incredible. After a little bit I laid back, which normally was the sign for her to start sucking my cock. She did, for a while. After a few minutes she crawled up to me and whispered, "can I suck his dick?" I said "ok" and she then turned around, slid his underwear down his legs and started going down on him. I couldn't really see his cock in her mouth because it was dark in the room, but I could see her head going up and down. After watching for a while I sat up, spread her legs a little and started fucking her. I lasted 1 minute. I came inside her and then laid back. I never lost my hardon because I was still so turned on.