My first and still most intense experience happened what I was 18. I had been dating this girl, Tania, for a while. She lived with me in my apartment outside Portland, OR.
Our good friend David would often come over, sometimes with some other people, to hang out for dinner or to watch the Winterhawks (any hockey fans?). As we grew closer, we started swinging with David. Tania was especially fond because we has marginally larger than I was but moreso because he had way better stamina than I did (if I last 5 minutes, I'm a happy camper...)
She grew increasingly impatient with sex with me, and grew more and more desperate for David's cock. I didn't know at the time what cuckolding was (I hadn't even heard the word before lol) or how to process any of it...the excitement of having threesomes turned into humiliation. And then shame for being turned on by it...
The situation evolved to a point where David would come over 4 or 5 nights a week. He and Tania would fuck in the living room, often sleeping out there, while I would hide in the bedroom drowning in my own humiliation but also completely unable to keep myself from furiously jerking while listening to Tania crying out and moaning while David pounded her. She walked back into our room one time and caught me stroking. At first she looked mad, but then this creepy smile appeared on her face and she got really close to my ear and started whispering to me about how she likes knowing how much I love listening to them fuck, how much it turns me on. She stroked me a little while she humiliated me then giggled and went back out to continue with David.
At the time it was definitely not a positive experience, since I had no clue how to process what I was feeling. It took me several years to finally figure that out. But now, looking back on it, I find myself wanting to experience it again (knowing what I know now). Just reminiscing about it makes me strain against my cage...