I was 17 and been with my GF for about a year when I found her on top of a heap of dirty laundry in the basement on a home party with a guys hairy ass pumping between her widely spread legs...
Right up to that moment I thought that I would scream and rage and dump her, but instead I just stood there and looked wide eyed on the guy that was fucking my girlfriend with a deep jealousy mixed arousal I never had felt before! I still don't know why I found that so incredible arousing but I did and I still do.
I had my very first sloppy second a couple of hours later... And three weeks later, on another home party, I found my girlfriend in a bedroom sitting topless on the floor sucking the same guy that had fucked her. If it was my GF that had sucked him for awhile or him in shock when he saw me standing there I never got to know, but his cock suddenly jerked and a huge blob of cum splattered in my GF cheek, on her neck and down on one of her naked tits and just to prove to me what kind of a women she really was she just turned her head, opened her mouth and let the guy squirt the rest of his cum inside her mouth... and she swallowed all of it without hesitation at all...
We got our little talk after that and about two hours later, in another bedroom, I watched the guy that she sucked off when he fucking my GF in front of me, he used her as the little whore she was. Three weeks after that I let my best friend fuck her on a tent trip, he ended up fucking her the whole weekend and fucked her almost as much as me in the next three years we was together after that, among others she also fucked....
That's how it started for me... And I still loves to watch my wife fuck with her lover... Watching her getting used...