This whole thread really was wonderful to read.
I am new to poly as well but I can relate to so much of it, expecially the first few posts. My advice is, if you truly are poly and she truly is mono, it may be best to end it now. Don't put aside your feelings,
My gf and I discussed poly because I was interested a few years ago, and she was not receptive to the idea at all. The resentment grew, I stayed with her, and am now finally about to break up with her. The unhappiness of these past few years was really unnecessary and maybe I should have gone through with it then. Now I have let things go way too far and am now about to lose one of my very best friends.
I know the idea of losing someone you love is scary, but the longer you let it go to worse it will get. You can't pretend to be someone else because of someone.