I am a 20 year old straight male, my girlfriend is almost 18 and super gorgeous. Some would say she's out of my league. We have been dating for almost 2 years now and we have been happier than i could have imagined. We have had a pretty good sex life in my opinion up until about a month ago. We were fooling around and she seemed to be getting frustrated. When i asked her what was wrong she said nothing, and that she didn't want to hurt my feelings. However, i persisted. She told me she loved our sex life and that she thought my penis was fine size, but she likes a little bit bigger than i have. I didn't really know how to handle that, it kind of shook me in a weird way but i acted as if i wasn't offened or hurt and we just went to bed awkwardly. The next few days were pretty much typical and we didn't really mention what had been talked about until the end of the week. She had me over for dinner and explained to me that she wanted to try having sex with other people. She wants big cock, and i admittedly am on the smaller side. I was very reluctant at first but she convinced me to allow it if i watched. We planned for her and her friend to come over to my place next weekend and we'd go from there. All week i was dreading this. I was scared, upset, humiliated. I was realizing i couldn't satisfy her. She wanted more than i could give and it made me feel so horrible. Finally the day arrived and i was actually feeling better about what was going to happen since i had all week to ponder it. I asked her to just have a real talk with me and she admitted, she thinks my cock is small. She loves me and even loves the sex we have, but she wants a guy with a big cock. At this point i was ok with it. At around dinner time her friend showed up. He was a lot better looking than myself and had a confidence i've never had. He wasted to time getting to business and after greetings and pleasantries he pulled her down onto the couch and started aggressively making out with her and touching her. I didn't know what to do. She seemed to be enjoying herself so i just kept quiet. Eventually the kissing graduated into her feeling his cock over his pants and i could already see he was pretty big. He quickly took off his pants and exposed his giant throbbing cock and the look on her face was priceless. She began to suck it lick and stroke and she was loving every minute of it. Honestly so was i, i loved watching her please another man. It turned me on in a way i cannot explain. She was loving every bit of it. She then leaned over and asked me to come to her and suck it with her. I don't know what possessed me to do so but i immediately went to my knees and began to suck his cock. I could barely fit it in my mouth and he was forcing my head down and making me gag. My girlfriend was so excited by this. She was taunting me saying that i could never be a man like him. That he was going to fuck me like a bitch the way i fuck her and that i had to take it.. That was where i was no longer ok with what was going on. I didn't want that at all and she was bent on forcing me into it. After going back and forth she rose her voice and told me that my small cock is not enough for her and that if i wanted to keep her i had to let him fuck me. So i bent over and prepared myself. I could feel him poking at my hole and i felt hot and nervous. He lubed up himself and then they both licked my ass and lubed it up. She looked me in the eyes, gave me a kiss, and said she loved me as he grabbed my hips, pulled my ass towards him and put his big cock in my ass. He wasted no time at all and started pounding away and all i could do was let out girly little whimpers. In all honesty, it felt so good. I was feeling pure ecstasy as he thrust in and out of me harshly and grabbed my ass and spanked me in front of my taunting girlfriend. He was laughing now as he pushed me down on the bed and drove into me harder and harder. He then nonchalantly pulled out and busted his nut on my ass. My girlfriend licked it off me and that was it. We awkwardly said goodbyes and that was it. Since then, we have resumed our normal lives and things have been nice. She loved watching me take a cock and be her bitch and i really liked it. I have come to the conclusion that this is the role i have been given and i accept it. My girlfriend turned me into a bi bitch.