You're talking about it. That's the good thing. Of course, I'm sure you know that you cannot expect one conversation to resolve it all. Think of it like an egg that's been cracked open slightly -- each talk will open you both up more.
For your next conversation, you may want to focus on the issue that she thinks this is a problem or sickness to be cured with therapy. Get down to the nitty gritty and ask what her concepts of monogamy are. Make sure she knows that infidelity and cheating are not what you want. You might want to talk about how we can love more than one friend, why not more than one intimate friend? Maybe find a book about poly that you're drawn to and share it with her to read.
I would, if I were you, attempt to have at least several more conversations about this with her before you two go to therapy, because that will seem like you agree that this is some kind of flaw in you. It's not! However, if you do decide to seek counseling, see if you can find a poly-friendly professional, or at least someone who is familiar with and not against alternative lifestyle choices. Maybe you can enlist the help of that good friend you mentioned in your first post to find someone for you. You don't want to wind up in a counseling session with your wife and therapist both wagging their fingers at you, so to speak, and making you feel wrong.