I agree with everything Redpepper has said and she has covered most points.
This is a great forum for anyone involved with a poly person. You now technically fall into the category of "mono" in a poly relationship and we are a bit of a niche group here but there are a few of us. I also have a blog dedicated to the topic polyamorouspeople.com
I felt like you on and off for a couple of years but once I started getting help via forums and from people who had experienced what I was experiencing things started to really turn around.
Mono/poly relationships aren't easy but they can be very successful, you just have to open your mind and your heart and have a partner who is prepared to work with you.