Welcome to our forum.
I'm sorry you had to find us under such difficult circumstances. It sounds like you and your wife have some pretty heavy issues to work through. A poly-friendly counselor would be good to go to if the two of you could swing that.
I'm also sorry your wife isn't talking to you right now. But there may be hope if she's at least willing to talk to you tomorrow (Sunday).
Polyamory isn't a bad thing per se, but cheating is, like, not okay. Additional relationships are supposed to be carried out with the knowledge and consent of all concerned. I'm assuming your wife figured you wouldn't say yes to a poly arrangement anyhow, and yet she still wanted to stay with you, so she kind of chickened out on telling you about it. Doesn't make it okay that she did that, but that's probably what was going on.
I think it's very big of you to open your mind to this idea, in spite of all the drama and sneaking around. For what it's worth, there's a great deal of help and info to be had on this website, so you are in a good place if you want to learn and try to understand polyamory.
First things first, you have to find out if your wife is at least willing to stay with you (and communicate with you) at this point. Next, you have to find a way to work on the problems in the marriage. As I said, a counselor would be a good idea. Once those two things have been addressed, you can then talk about the idea of her (and you if you want) being poly.
I hope things go okay when you talk with her. It's possible she has some kind of deep unhappiness in the marriage, or maybe it's just her being chicken about admitting to you of her poly feelings.
Please keep us posted on how things are going, and let us know of any thoughts or questions you may have.
Love means never having to say, "Put down that meat cleaver!"