I've been in approximately your place, polymusing. I knew in my heart that I couldn't do this whole monogamy thing, but I also knew that I couldn't cheat as I hold honesty in the highest regard. When I first tried tell my husband about it, he stormed out of the house. That was in July. By September, he accepted that this was non-negotiable to me, but he wasn't sure that he could accept it. Then he did research and read. Last weekend we sat down and talked again about it, to lay down "the rules," which pretty much consisted of not dating people that he couldn't stand (not that there is anyone in that category, but in general). We talked about my highly inconvenient current crush and now he lovingly teases me about it.
In short, when there's life, there's hope. Everyone moves at their own pace, particularly when they are scared or confused.