I've been going through a lot of what you've been going through as well Freetime. One person on here said in my blog thing, that I was mourning. Mourning the loss of what my marriage was. It made a lot of sense to me. Even if you said that your wife can't be poly, and she was totally cool with that, it wouldn't change anything. It would still be there, and you would know it. She wouldn't be as happy as she could be....
It's an incredibly hard thing to overcome. I've been dealing with it the last few weeks myself. I think I'm finally starting to give it up, as far as trying to hold on to what we had, and go forward with what we have. It hasn't really changed anything at all. Only thing that has changed is how we feel about each other, and that hasn't been negative in any way.
It's going to take time to find a comfort area for everybody. That's just something you are going to have to figure out on your own. I still don't even know where mine is really. I'm still struggling with everything, and I still have back and forth days. I think there have been days where I started out cool with poly, then didn't want it, then for it again, and by the end of the day wanted nothing to do with it. So it seems the back and forth thing is pretty normal.
Are things going to fast for you? Is that why you want to fight it so much? Just remember that you have as much of a stake in this as your wife. If you need to start out slow, then so be it. Hopefully you can communicate that, and hopefully your wife will agree to it as well.
Good luck, and remember that your wife still loves you very much. Otherwise she wouldn't have asked you to go along with poly!