Hi, May. I never read your thread though I have seen and loved your posts in MLC. I just took a quick gander and do not know all the details so take my words with a grain of salt.
I stood for seven years, ten if you count when I started feeling unloved. I was basically a saint in the face of his infidelity, lying, stealing, etc. I kept believing in the man I thought he was and laying my grief at God's feet.
I don't regret that but I did discover what I had been told all along was true. That some things can't be talked out, and you can't expect healing to come from your spouse.
To me it seems like you are straddling three fences. There is a financial fence, and the part about the kids, as a post nup. There is the reconcilation fence. And then a divorce fence.
I think you need to commit to one side of one fence for a time. And it seems like you want to keep the marriage.
So my advice would be to declare a moratorium on R talk and just do IC. Make an actual rule not to do that and just to have fun for a while.
When the thoughts of the AP come your way, remember that they are from the darkness. They are a very real wound but your H is not going to be able to heal that wound. I don't know how you heal that wound without God, but if you don't have a faith life, I think you just have to keep giving over that pain to time and the universe. Expecting that your H will be able to say or do the right thing to heal your wound is a pipe dream. You can only hope that you build a new history with him.
If you don't trust him, you can't think he can fix that. He can destroy your trust further but only you can decide to trust again. In faith world we say that we don't have to trust the straying spouse because we trust God. In a secular sense I would say that this means making peace with NOT trusting him and knowing that you will be okay no matter what he does, and deciding if you want to hang out with this guy and go on dates and enjoy the kids together and then COMMIT to that and keep your doubts and fears and the rest between you and your journal, your IC and a daily hike into the hills overlooking the sea where you literally talk out loud the entire time and give all that pain away. If you don't think you can do that until you are sure he is done with her, then commit to that instead, tell him you can't wait to see him when he is at that point and you will put things on hold til then and just work on yourself and your independence.
A post nup might seem like a good security blanket but it seems like you are imagining it will fix a lot of things, and I am not sure about that. Maybe you can just divide all your finances for now and work on that when you know more.
I used to imagine murdering the AP. I hated her so much. I didn't get rid of that feeling. I just kept asking God to heal it. I think he did, a little, but they also I think broke up, and my H became so monstrous that I can't ever R with him again so I almost feel sorry for any woman who would get sucked into his vortex. But I do pray for him to be healed, and I wonder if you can just keep giving that responsibility for fixing your H and for healing your very real, very deep, very painful wound to the universe. It's too big for you, for any of us. I don't know if you saw this in my thread but a priest once told me that the pain I felt should not scare me, the way that when you have a broken arm and it throbs, you don't think it is breaking again. You know it's already broken, and the pain is coming from that already broken place. This helps me a lot to deal with my pain and not expect that any human being can fix it for me. It just has to heal.
I believe I will see the bounty of the Lord in the land of the living. Wait for the Lord with courage. Be stouthearted, and wait for the Lord.