When/how did you discover

My first realisation was when my fiancée revenge cheated with my best man the early morning before the wedding. We were only 19 and had a party the night before. At this I had felt up the tits of a mutual friend who was up for the wedding from Gloucester. She was a sexy 17 year old girl who was staying with us. Mary was understandably furious but I did not realize how angry at the time.
I got blind drunk and passed out on the double bed. Ash the best man was to sleep on a Z bed in the same room.

I woke to a gentle feeling of being rocked awake. I looked around and saw Mary with her nightie pushed up to her neck.Her pert C cups were bouncing around and Ash on top of her fucking her hard. She was moaning. From growing up as best friends I knew why as Ash was much better endowed than I was. I blearily said what the hell. Mary looked across at me and said " Don't ever disrespect me like you did last night or you'll be sorry." She smiled a satisfied smile and turned to Ash and said " You going to finish what we started? " Ash was embarrassed but still inside my fiancée. Seconds later using her internal muscles Mary milked Ash off inside her. He fell forward and grunted. I looked on disgusted and tried to think what to say. Then I realised that I was erect. Maybe it was an early morning wood but I think the situation got to me too. This was the first time I had seen anyone else have sex and though I felt jealous as hell and thought about calling the wedding off, in the end I went through with it. I married a girl still with come from another inside her. Ash and I were never as close again as he had broken our bond of friendship. 9 months later Mary left me for a man she met in a nightclub where she did a second job in the bar.
 
I was still friends with one of my exes. She lived in a different town at the point and she was just telling me about her life. She met a guy and I asked how the sex was. She gave me details of their sex and it was hot thinking about this girl I used to fuck being with someone else.
 
During our undergrad/college years, when KK'd broken off our engagement. I was obsessed with the thought of her fucking other guys - couldn't get it out of my head. For a while it was the only way I could get hard and cum.

We reconciled, got married, took about twenty years to make it real.
 
We fantasized and role played alot during foreplay while in college. I am not well-endowed and truthfully have always cum way too soon to give her the kind of satisfaction she craved. We'd play a game while out at dinner or shopping ... one of us would comment on whether a guy was fuckable. But we never discussed going the extra step to make the fantasy and game real. Fast forward two years and we graduated, got married, and moved to a smallish town near the North Carolina coast to start our careers and life together. Totally unexpected, but a good looking high school senior hung out at our apartment pool and within a few days was making small talk with us (her). Stacey was quite stunning - favored wearing a tiny (for the early 80s) black string bikini which he really liked. We started fantasizing about him fucking her - and she got more and more into it. Wasn't long before he was rubbing suntan lotion on her and getting pretty free with his hands and fingers. Started innocently touching her as they played in the pool. Mostly while I watched from our apartment window but at times in my presence at the pool. Eventually we invited him to our apartment to hang out - watch sports on TV, cookout, etc. Stacey and I talked, and at her request decided to let him feel her tits (halter tops and braless summer dresses) and kiss. I watched the first time at their image in the picture frame glass that gave me a clear view of the kitchen. He approached her and they kissed. After a few times, he touched her breasts and put his hand up her dress to feel her panties. She shared the story with me - I told her I'd seen most of it. It turned us both on. Wasn't long before Stacey asked me if I'd be OK if they fucked. I went shopping one weekend morning and left them alone in our apartment. They fucked for the entire year and off and on for a couple of years when he'd return home from the Army. Started us on a 40+ year lifestyle of swinging, cucking and mostly hot wifing.
 
I think it has been a slow evolution. It probably began when I was younger and I had strong feelings for a girl, we fooled around but were never officially together. One time I took her to a party and she hooked up with a bigger, stronger and darker south american guy in front of me and all our friends. It was humiliating and I was visibly upset. Now the memory turns me on. She had also had a black ex boyfriend and when I asked her about what they did together, instead of protecting my feelings she told me how much bigger he was than me and the stuff she would let him do to her. She would only ever let me rub her pussy through her panties and would occasionally jerk my cock but never to the point of cumming. I think some young ladies learn from an early age the power they can have over males and she enjoyed teasing me. If only I could tell her now the path she started me down.