I suggest that you do a search in the tags and stickies on here under cheating, and affairs... it will bring up a lot of really good threads that a lot of us have already been talking on and might help.
In a nut shell, having read the other posts and agreeing with just about all that is said, I think if I were you I would end your engagement right now, tell him what is going on and brace yourself.
I'd be finding a place to stay just in case, make sure you have your finances in order as you might have to take care of yourself and say good bye to man two for a bit.
Then I'd tell man one.
You've got some serious work to do I think.
number one? I think you need to change your attitude. You are mainstream, you are cheating. That is mainstream.... leave the poly thing alone for now, you have a lot more to think about... building integrity, respect, honest open communication and empathy is what you should be doing as these are the foundations of poly, at least to me...and I know many others that would agree. You not only have none of these it seems, you have less than none... that is a lot of work to do.
Poly is by the closest definition for most the ability to love others in an open and ethical way... you are not even close, so I'd be getting on it.
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