Originally Posted by Idaho
(its not that he wanted to go outside the group, he hid it from both of us and lied to us)
That rather implies that he did want to go outside the group; he just had no idea how to tell you. It's sad that he didn't feel comfortable bringing this up, sadder still because now his actions have broken up what sounds like quite a functional, happy group.
I am having jealousy feelings again because now shes wanting to be monogamous with my husband and I do not understand why that's bothering me so much.
Weeeeell, it's only a problem if he wants to be monogamous with her as well.
I sound flip about it, but really, polyamory at its heart means that your husband doesn't have to choose. Him being her only partner does not negate him being partners with both of you. I'm "single-plus" right now and I certainly don't expect anyone to give anyone else up for me.
I think you've just been through an intense breakup. If I understand you correctly, you weren't involved with the woman of the other couple, just the man; his leaving, especially in that manner, is a blow. Naturally you won't bounce back like so much elastic.
Give yourself time to heal, but do remember that perhaps the other woman's way of healing is to cling to the people she has left--and that includes you! Will working on your friendship help you see her as less of a threat? She'll be adjusting to single motherhood now; you might bond over the children, if you like.