OK jumping right in here - Sagency: Where does your belief that there are "many happy poly-mono relationships" come from? I recently did a survey with the polymono and living polymono group sites on Yahoo(they cover monos with polys and polys with monos). Maybe they are places of relationships under stress, but what came out of that survey was a resounding lack of working. More monos responded than polys but this was the result: In relationships where the polys were active the monos weren't happy and in relationships where the polys were inactive or minimally active the monos were happy or happier but the poly partner was unhappy.
I can understand that the woman in this relationship feels that she has to 'convert' to find real acceptance. After three years in a similar relationship I am coming to the same conclusion. Initially I was fine with it but it's actually a pain in the neck. I would almost say I am besieged by married guys misunderstood by their partners who say they are poly but don't actually realise that honesty is part of the deal.
I know of only one successful poly/mono on here: Mono and RP. Trucker Pete and Indi are sort of but Indi has described himself as "mono by default" so I don't know if that really counts. If I have missed you and you do consider that you have a successful poly/mono relationship please come forward and share how you are achieving it. There was Vodkafan but I haven't seen him for a long time and I would say that my acceptance of the situation has gone way down since I gave up alcohol.
Sorry if I've hi-jacked this thread prommat but from my experience what you are going through is par for the course. Your girl friend's responses seem emotional rather than rational and I think this is a symptom of loving someone who loves differently to the way you do.