The first part of this story is here: http://www.reddit.com/r/gonewildstories/comments/3by4eg/first_time_as_another_couples_second_male_very/. This second part gets right to the sex, but the first part has the context that led us to this point, which you may want to read, because you may relate to some of it.
The evening has become in my memory a blur of hot sex, with many standout parts to it. Ryan and I kissed and touched up and down Vivian’s body as she lay on the bed, our kisses getting wetter and harder as time went on. She turned around and we all made out with each other, our tongues and hands all over each other, our limbs intertwined. Ryan and I were hard, Vivian was wet, and our hands freely went to work exploring each other’s erogenous zones.