As I stated in my first post, I backed off because I AM concerned that he has not told her and how she will react/feel. Sure, I have an attraction for him, but I am by no means NOT concerned about her. This is why I posted to begin with, to learn more about the agreements, meetings and guidelines when dealing with these issues and because I was bothered by the guilt that I felt for being with him to begin with.
I was not aware of him being in a poly relationship with a girlfriend until after we had already been together. I assumed when he said, "you should meet X" that he was talking about a friend or FWB. I do not like the idea of him waiting to tell her, but as someone else stated, I am not fully aware of what is taking place yet in their lives (they do not live together) and for all we know, she could have just dealt with a death or some other traumatic experience.
He stated he would tell her after their trip and all I can do is hope he tells her the truth at that time (few weeks at most). What else can I do? If I hear from HER that everything is good, then great. Maybe all four of us can get together, who knows. If not, then I don't need to be with anyone that is dishonest and keeps things from a partner that will upset or hurt them.
I am a very compassionate person and it bothers me to death that she does not know. But I'm tearing my hair out about what "I" am supposed to do about it from here. I've backed off. All I can do is learn from whatever happens.