Another followup. I know religion isn’t a popular thing with poly, but up until recently it was very important to us. I took vows to my husband before God to forsake all others. I don’t know if he’s ever going to want to have sex with me, even if he gets his itch scratched. And if he does, I don’t know if it would be worth it if he’s thinking about his other girlfriends while he’s with me. If I leave, it affects our daughters negatively. Autism needs stability. I keep going in circles. Sorry.
First, a challenge to your assumption: there is no communal polyamorous consensus that religion is unpopular. (I personally am poly and also a devout Christian with plans to go into the ministry someday.) Like monogamous people, polyamorous people come in all types. If you believe that being polyamorous would conflict with your religious beliefs, and contradict your marriage vows, that is completely your business. But it is not necessarily true that polyamory is incompatible with religion.
Nor is it unheard of for marriages, in and out of the church, to change, grow, and shift over time. You and your husband are not the same people now as you were when you made your vows over 20 years ago, and I think it is okay to revisit certain things to ensure a healthier, happier present rather than holding yourself to something determined in the past. If you two haven’t already tried marriage counseling, I’d recommend that as well.
But again - you don’t sound like you’re interested in making that shift. And that’s okay. If you want me to try and convince you, let me know. Otherwise, that’s not my place. It sounds to me like you want out of this arrangement, because it has become untenable to you, and your biggest argument for staying is your children. If you want to separate, my advice would be: separate. You have your life to lead and your own needs to fulfill, even though you are a mother. And staying in a situation you find miserable for the sake of your children will likely end up hurting everyone in the long run.
It is not necessarily true that children are better off with two parents, if those parents staying together creates a difficult or unhealthy situation. I am not a parent, but I was raised by two people whose marriage was rocky and painful, especially by the time I was a teenager. I often found myself wishing they would just separate already. Being at home with them was unpleasant, and I took away a lot of toxic ideas and fears about relationships from watching them. If you become unhappy, resentful, mistrusting, or distant, it may have more of an effect on your children than a separation might. My suggestion would be to talk to whatever specialists know your daughters best, and get their advice on how a separation might affect the girls and how to minimize their stress.
It is true that your daughters have special needs that might make a divorce especially hard on them. But after a separation, they would return to a new routine and stability rather than staying in a house with two parents who were unhappy with each other, creating a constant state of instability. With the right attention to their needs, therapeutic intervention, and amicability between you and your husband, it would be entirely possible to separate with the least amount of upheaval possible.
And it sounds like your husband continues to want you as a co-parenting partner, which would make things much easier. I know plenty of couples who, after having children together, discovered that they made much better co-parents than lovers. They raised their kids together after they stopped being together romantically, and the kids that I know who came out of those relationships were fine with the arrangement. One told me she knows her parents as good friends and it’s “weird” to think that they were once romantically involved. It is often easier for polyamorists to imagine and maintain this kind of model, which may be why your husband brought that term into the mix.
You are the only person who truly knows what’s best for you and your family. Just don’t forget to take your own needs into account. I am so sorry for everything you’re going through.