Disclaimer: I am not that experienced either in the world of poly or in the world of relationships.
Having said that, it doesn't look like this woman is capable of the level of honesty required for a poly relationship. She didn't just cheat once. There have been relationships where one partner cheated and they were able to work through it and save the relationship. But that is some SEVERE cheating you're talking about right there.
If you want to save the relationship, you need some very good, very thorough relationship counseling. Poly shouldn't even be on the table until you've worked through all the issues and addressed WHY she cheated and WHY she was completely and utterly dishonest with you. And my feeling is it will probably take YEARS and there's no guarantee that it will even work. Because it will only work if SHE truly desires to make a change, a deep-down change, not just a look-I'm-behaving-better change.
Personally, I would straight up end the relationship. You love her, yes, but do you also care about yourself? Because staying in a relationship with a person you can't trust is NOT GOOD FOR YOU. It's not good for her either! Because it's just enabling her to avoid the fact that she seriously hurt you and did you wrong.
Either you go into counseling so she can face that fact and deal with it, or you leave her ... so she can face that fact and deal with it.
Edited to add: I do have experience with leaving someone I love because I can't trust them. I'm in the middle of doing that right now. It hurts, but if the untrustworthy partner refuses to deal with their problems, leaving is the best thing for both of you.
How old is your son, by the way?
Independent polyperson seeking friendships, in which physical intimacy may or may not develop.
I do not wish to attach to any particular person. My love knows no limits.
Last edited by SkylerSquirrel; 10-14-2012 at 10:26 PM.