My heart goes out to you, Sourel. Bless your heart. I have been the cheated on spouse, although not in the heart-wrenching circumstances you describe. My deep condolences for the loss and grief you've experienced lately, and for the pain your husband and his mistresses have inflicted on you.
With all respect to Loving Radiance, Maca, GreenGecko and their tribe, their situation is the exception rather than the rule. Most people are neither willing or able to put in the monumental effort they have invested in making the transition from infidelity to polyfidelity. And even now, they continue to face challenges on that front.
If I were in your situation, I would drop that cheater like a hot rock. Not because he had feelings for someone else, but because of the disrespect he had demonstrated for me, and for the destruction of the trust we had built together.
Explore polyamory if your heart leads you to, but you deserve trustworthy partners who respect and cherish you. This group has not behaved in such a manner as to be worthy of you.