I don't post very often (I am in the MLC section) but so much of what you have written in your last posts have resonated with me.
Your fears are mine - now that there is an OW, despite all the advice to not give her head space, I cannot help but feel that with her present, reconciliation is impossible. It is strange how I imagine their relationship as ending happily ever after but cannot manage to truly believe that there is hope for SO and I. And the more she get integrated into his life, the more I feel "us" slipping away. It sooo hurts when I hear that she is starting to meet friends and family. Feels more permanent somehow, doesn't it?
I agree with Tori - I think many of us feel like we were thrown into a pool of ice water when we realized that we played some role which brought us here. I don't accept the full blame for this nonsense, but I do know that I could have been better - much better. I think we'll not make the same mistakes again.
Of course, my MLCer thinks we're buddies now, so my sitch is a little different now but I can remember clearly the feeling of the invisible wall between us. Where once love radiated, there was nothing. Like sitting next to a stranger on the bus.
I have not read all of your thread, but you seem like a remarkable, strong and aware person. Your H should consider himself lucky to have you.