It was during my early college years, around 19-20yo.. I had accepted my bisexuality and I had already came out to my girlfriend and close friends. One night a company of our closest friends, we had some drinks and a hell of joints, so we started fooling around, playing "sensual" games. My girlfriend had been penetrated by a dog during this "sensual" games session, and I had my first oral engagement with that dog, which after that he came behind me and started rubbing his cock against my ass, without ever penetrating me. I was so aroused that I almost cum. The next day the guilt I felt was terrible. But, it was my girlfriend who tried to calm me and make me feel not a monster or a creep. She was the one who made me to accept this act.