Hands down the the most erotic relationship I ever had was when my best friend's girlfriend invited me to participate in their relationship. She liked her men big, and I knew that he was large... though I didn't know how large until I joined them in the bedroom. Although she adored him for his big cock, it was too big for anything outside of vaginal intercourse... Her lack of satisfaction stemmed from just that... she was obsessed with sucking cocks (especially deepthroating), and he was so big that she couldn't get the head into her mouth. She also found herself missing anal sex, but there was no chance of doing that with him. So the two of them approached me with the prospect of a) fulfilling her fantasy of being with two men, b) having a man with a smaller dick that she could suck on, take on anally, etc.
Our very first romp in the bedroom involved inserting me inside anally before taking him vaginally at the same time. The experience was amazing and as he entered her with me already inside, I felt the pressure of his enormous cock crushing against mine through her stretched walls as I felt her anus clamp down hard around me. We started slowly and the three of us soon found our rhythm together. She remarked on her amazement of feeling our two hard cocks bumping together through her walls as I felt every thrust and throb of his cock through her and understood for the first time a woman's delight in the awesome feeling of completely being filled. The two of them started to come
together, and feeling her contractions as he throbbed and ejaculated inside her put me over the edge.
Our relationship continued for a long time, as our respective desires were very compatible. He didn't care for giving or receiving oral whereas she did, and they were both delighted upon learning that I couldn't get enough of it. I loved going down on her to get him ready for him, and she loved deepthroating me while he took her from behind. I especially liked being her her mouth while she orgasmed with him, after which she always sucked me dry.
Although she clearly preferred the big cock for vaginal intercourse, she sometimes she'd take me vaginaly for variety and a bit of a tease. It was very sexy and a little intimidating to feel how loose she was, especially when she'd had him inside before me. It turned me on when she'd giggle with me inside., amused at my passionate but futile thrusting efforts touch her as deeply as he had.
She described having two cocks - one big, one small - as the most perfect arrangement possible, and I couldn't have agreed more. Never before nor since have I ever felt as much satisfaction and adoration as when my cock became the object of her desire and used in the fufillment of a woman's forbidden fantasies.