Dear, sweet Mahogany,
I don't think you should indulge in feeling guilty anymore at all. So, lovingly, I say: Stop that!
Good for you for standing up for yourself!!!
Really, you tried your hardest to live with an affair turned into (so called) poly, but in your previous threads, it became evident that Crunchymama was not taking any responsibility for what she and your husband put you through and it seemed she was a cowgirl. You should be commended for making the effort that you did. Your husband cheated on you while you were pregnant with twins and focused his attention on his mistress, and she came here trying to paint you as the bad guy.
Do not waste time and energy feeling guilty. Now is the time for you and your husband to repair your marriage. He betrayed you and your trust. It is a good sign that he is willing to let her go as a lover in order to stay with you, but what else will he do? Does he expect your relationship to just get better by itself? You have every right to ask for, and perhaps even demand, better treatment by him.
I would suggest therapy or counseling and a clean break from her, for the two of you (why is he still even staying in touch with her??? It's like he's addicted), at least until you both have made some progress in healing the wounds he caused. I know he comes here, too, so it would be good to hear his side, but I'd like to know if he has stepped up his game as a father to your babies. You have two infants who need your attention. Dealing with the drama of his affair and trying to handle it all as a poly relationship surely added to the stress and strain of being a new mommy, along with the normal exhaustion that goes with it.
Personally, I think your husband owes you big time. You were treated quite disrespectfully and then expected to go along with whatever he wanted in the end, without any consideration for you. He didn't even acknowledged being a new dad when he posted here - what's up with that?? He should be doing all he can to make it right again and EARN your forgiveness.
You don't owe Crunchymama a thing, in my opinion. She tried to drag you through the mud and made it seem like she was being victimized by you. And then stopped posting when people here said she should own up to her part in the betrayal your husband did. You have better things to do with your time than worry about her -- she never worried about you.