I do have a couple of things to add. I just read GalaGirls post. If this really is just about dishonesty then I agree with the boundaries she is talking about. It's up to you to enforce them, and then decide for yourself if you still want the marriage if she continues to break them.
You two had a rocky start with the poly, and you mentioned codependence. That's a heavy load. I'm still very curious about what is causing her to be dishonest - if it's related to that rocky start. Only she really knows that.
If you want the marriage and you're still willing to work on it with her, and you two find what is really going on with her to cause her to cheat, and she is willing to look at her own behavior (a lot of and's), you two may be able to get beyond this quickly without the stress of wondering if and when the next time is she will cheat. That would be a very good thing. It's up to you if you want to talk more about this with me. You'll have to be willing to talk about it in depth.
If so, let me know anything else you think is relevant, and we will take it from there another time. If not, I hope you get what you need from others here.
It's time for me to log off.