I am glad TP and Indigo responded; I wanted to, but since I've yet to be in a situation like yours, thought it best to wait for others' input.
I agree that your wife likely feels threatened by your revelation and is focusing on the sexual aspect that she probably sees as the reason why you want to explore polyamory. If I were her, I'd be doing the same thing, trying to make you "see what you'd be missing" if you went elsewhere, and give you reasons to want me more and forget about this "silly" idea you have. It is very easy to feel totally insecure about being desired. Plus, most woman know that a man can become pretty drunk on sex, which puts them in better shape to be convinced of something (that's just intuitive, not necessarily manipulative).
She is probably absolutely terrified of your choosing someone else over her, or of leaving her. Terror is extreme fear, but the quality of being unseen or unknown sets it apart from horror, which is what we feel when confronted head-on and we see what it is we're horrified by. In reality, we never really know what the future holds, but when someone has counted on something to go a certain way and has expectations that life will continue on in a pretty predictable route, the unknown can really throw us off-balance completely and terrify us to the core.
Plus, I think that your "confession" has thrown her for a loop; it doesn't make sense to her. She is grasping at the most obvious "reason" she can find for what she sees as a complete 360° about-face on your part, of course not understanding how you've struggled for so long. And that it must have something to do with her desirability or your sex life, would be the most obvious to a woman, I think. She might even be surprised that you still want to go with her to a therapist, if she believes she's done a "good job" of convincing you that she is all you need.
The trick is to let her know that the increased ardor and closeness you two have been experiencing in the last few days is something you appreciate, are thrilled with, and want to continue, but that it isn't what has prompted you to broach the topic with her.
But no one here has really answered your question yet, I don't think, of whether you should continue in this blissful state for a few days and wait until therapy to remind her of the changes you want to see happen, or do you bring it up now so she doesn't get her hopes up too high that all you needed was a reminder of how good it is with her. I don't see how it could hurt to gently and lovingly tell her at the next opportune moment, if it feels right, "You know I love you, and we still have a lot to talk about."