mmm, at least some parts of your story sound VERY familiar. i have only recently split from my lovely, beautiful, loving wife because i have come to the realisation that i am fundamentally poly. she, however, is entirely monogamous. as far as i could see it, the only options were for her to compromise on something she held as axiomatic - impossible - or for me to do the same - equally impossible. the result: i pushed her away and left her with my beautiful 16 month old (as of today) daughter. brutal. heart-wrenching. destructive. but necessary and (i hope to god) better in the long run for all of us.
imho: poly + mono = too-major-compromise-by-someone = destruction = death
novisse et notus esse; amare et amari.