Please don't feel guilty - you have nothing to feel guilty about. You haven't betrayed your partner simply because you're finding yourself with certain sorts of emotions. Keep reading the posts on this forum - you'll see that there are lots of polyamorous people and that there's no need for a person to feel guilty simply because he or she happens to be poly. (Even if you're the kind of poly person who truly "can't be monogamous", there's nothing to feel guilty about unless you actually cheat on/betray your partner, and of course, you haven't done that. But even if you had, the betrayal would be the proper reason for the guilt, not
the fact that you're poly.)
You'll also find a great deal of helpful advice in the forum - for instance, advice concerning the importance of communication, empathy, patience, taking baby steps, etc. And you'll find examples of very healthy mono-poly relationships - if I were you, I wouldn't assume from the outset that you and your partner can't be in such a relationship - it may well be possible after all.
In my own case, my husband and I are separating in part because of our mono-poly differences, but there are other factors as well, and I have no doubt that mono-poly relationships can work. I just recently posted my story; if you're interested, you can find it here: http://www.polyamory.com/forum/showthread.php?t=10256
(I should warn you though, the post is on the long and wordy side
). In that post, I go into detail about how I figured out that I was poly and about what ensued between my husband and me. (You'll also see my struggle with guilt; that struggle is part of the reason I hate to see someone like you burdened with guilt.)
But in any case, your situation may be very different from mine, and ultimately, things could turn out very well for you and your partner. Best wishes to both of you!