Thank you both so much for your insight. It really helps. I've decided to sit down with him and have a discussion about the whole thing and see where it goes. I'm not extremely hopeful that it will go in the direction I'd ultimately like it to, but maybe we can move toward something that will feel like more of a compromise than a sacrifice.
In answer to your question, Mono, yes he knew that I was poly. He and I have been friends for a long time and he knew of the situation when I was married and how happy it made me. However, while he hasn't said this exactly, I think that he felt that it was something that was caused by what he feels was an unhappy marriage as opposed to something that was part of me. Unfortunately, I don't feel like there is any chance of him warming up to the idea. He said the idea of me being with someone else made him feel physically ill and he could never imagine being with anyone else. I don't think he's programmed so much as just naturally monogamous. Of course, sometimes the programming towards monogamy can be stronger than people want to believe...
Thanks again. *crosses fingers* I hope...I hope...I hope...that the discussion goes well.