PandaLover, I am very sorry that you are in this deeply painful and confusing situation. It's not your fault. You and your children deserve peace, respect, and unconditional love. I hope you don't mind if I quote you as I respond.

I'm putting together two points you made here:
He is in love with his 14 year younger affair partner....
and anytime we talk or are together I feel no hope, love, anything.
If you feel comfortable, take a moment and read this out loud to yourself. How does it sound? How does it feel to you? What might your future look like with a husband who loves another woman and does not bring you hope, love, or anything?

He has asked for an open marriage more than once and I have no interest in that.
This is a very important insight. Do you see how this is untenable? If you two don't perceive marriage in the same light (monogamous versus polyamorous) then I am wondering how you could continue the marriage? Neither one of you is able to give what the other wants or needs here.

I told him I think he should take a month with zero contact with either of us to really, truly make an unbiased, uninfluenced decision because there are 5 lives here that stand to be deeply impacted by whatever decision he makes.

I have a couple of thoughts on this. Unless I am misunderstanding you (feel free to correct me if I am) it seems as though you think this is his decision to make. But this is your life, married or not. You must choose whether to accept his infidelity or divorce him and start a new life. That is not his choice to make for you. I don't think the timing of the decision is the issue but that you seem to want him to choose for you. That might be worth reflecting on.

You also mentioned five lives that stand to be impacted by the decision he makes. I see it that three lives would be your priority here: yourself and your two children. And those three lives are already deeply impacted by the previous and current situation, right? You and your children are likely traumatized since his departure and infidelity, plan for divorce, and then wavering. You three folks are in limbo. And that's a very painful place to be. Uncertainty is so difficult. You cannot undo the past, what's happened has happened. Your power and peace will be in planning for the future. What future do you want for yourself and your children? I have a hunch that you know exactly what you want. Have you tried writing in down or saying it out loud? I want my future to be ____________________________________. I do not want my future to be _______________________________________.

He acts like that’s an unreasonable request that he can’t consider. So my question here is, is that a fair reasonable request with so much on the line here or isn’t it?
I would look at this from a different angle. Consider asking yourself why you are asking him this....why not instead ask yourself what you want and then slowly develop a plan to make that happen. Bring the focus and power back to you and your needs and wishes.

I truly don’t know anything anymore…HELP!
Trust me PandaLover, you know plenty! You are likely doubting yourself and struggling because you have been dealing with a great deal of stress and pain and trauma. Trauma does not make decisions or planning easy but things can be figured out slowly in time. I think the first step is to take yourself out of limbo. What do you need in order to make a decision for yourself? What would help you to do that for yourself?

You have very clearly stated what you want: a monogamous husband. He has clearly indicated, with words and actions, that he is not able or willing to be a monogamous husband. So, now you need support yes? To break away from limbo and figure out the future. Would you be willing to talk with a therapist? Not with your husband but on your own. Your children would likely also benefit from some trauma therapy and coping strategies to manage their stress and confusion.

You are struggling with a very human dilemma: choosing between attachment and authenticity. By authenticity, I mean living as you truly want to live...honoring your own value system. I think if you choose to accept an unfaithful husband, you will be unable to live authentically....it is a violation of your personal value system of monogamy, yes? Living without authenticity can have devastating consequences for physical and emotional health. That said, this situation is not easy or simple by any means. I understand. He is your husband. You conceived and raised his babies. Of course you feel confused and hurt and scared. You are human and you're dealing with major trauma.

I recommend finding some support. Someone kind and knowledgeable to help you work through these feelings. Instead of encouraging him to decide for you in a month, why not step back from him entirely for a while and focus on yourself and the children.

My situation was not the same as yours but I did opt to divorce a husband who could not give me the life I wanted. It was extremely painful and took time to heal but I have honestly never looked back or second-guessed my decision. I chose authenticity over attachment to someone unhealthy.

I hope this helps a little bit. I wish you and your children peace, hope, and a bright future! You deserve nothing less than that. Be good and kind to yourself. Rome wasn't built in a day. Take some time to think this over from your perspective.