Awww, it seems like the big poly tribe you often said you wanted is forming itself among the people you love and care about!! A loving family/tribe - isn't that what you always dreamed of? Brad and Derby - wow! And I would think that you'd be happy Mono is now open to poly, especially since you often said you could not understand his mono ways and could not relate to monogamy. He's willing to walk a few miles in your shoes and see how love can be expansive - isn't that a good thing? PN having a gf for the first time in a very long while, and feeling so close that he's considering being mono with her, wow again. The paths of love just keep growing and evolving. All we can do is roll with it and see where the river's currents take us. How powerful and uplifting that you are surrounded by such a beautiful loving network!
Are you feeling a bit like things are spinning out of your control? Is that why it's so overwhelming for you? Maybe the exhaustion is coming from trying too hard to preserve the same position you once had with all your loves. You were this impressive force, a woman who manages having many relationships, and now those relationships are expanding beyond your grasp, and you are one of many. But you are not less than you were before - you are still loved and wanted and valued!!
I know you are strong and definitely can handle some of your loves having new relationships, even with each other. The dynamics have shifted and changed, but it's not necessarily a bad thing! It looks to me like your poly dream coming true!
Get some rest, RP. Maybe sleep and a new perspective will help.