I hate the way this sounds but from everything you've written....you need to gently release him. If you hope to get him back, you need to release him now. He is telling you, over and over, that he needs to go. You need to listen. Honor his wish.
It doesn't make sense to you. I know that. But if you hold him, or struggle, or resist him, then at some point he will start resenting you. At some point he will block out all pleasant memories, and "it isn't black and white" will transform into "it was always black". Holding him tightly is making it worse.
He has this idea in his head that he has to go. I know it is against every fiber in your body that you should agree to break up your marriage, to separate. But that is what you have to do now. You have to accede to his wishes. If you want him back, ever, preserve what you have with him now by agreeing with him.
I know how hard this is. I know it is a nightmare. I know that you can see a simple path toward reconciliation - "let's just go back to normal life, go to work during the day, out to dinner at night... come on, we can work this out." Listen, I had all those thoughts too. It seems soooo simple to you. "Let's just not fight anymore." He can't see it. He can't do it.
You have made a good effort this far. No one should have to do what you have been asked to do. Yet you have worked hard to save your marriage. So far, no joy. The first principle of DBing is - do what works. What you have done has not changed your husband's heart. Doing it more, longer, or more energetically, will not have a different effect. You need to do something different.
At this point, he needs to go. Or at least he needs the freedom to go. He may go, or he may not, but he needs the freedom to do it. He feels the need, just as strongly as you feel the need to hold your family together. My suggestion is to let him lead his life. Let him make his decision and act on it. You don't need to agree, you don't need to help him, you don't need to be excited about it. But I feel like you need to accept it. The best you can do now is allow him to go, with a minimum of guilt and resentment. Preserve yourself and your relationship with him for another day.
You can show him you love him, without pleading for him to stay. This means, admitting you will miss him, but not falling apart. This means banishing the thoughts like "how will I survive?" You will survive without him, for his time away from you. You must, and so you will. If he will ever come back to you, then starting now, you will need to be strong, stronger than you thought possible, stronger than him. If you despair and flounder without him, it will only accentuate his guilt.
You are being asked to do something no one should have to do. It's sad, and it's not fair, but it is. It just is. It stinks. But it is up to you to take the lead. Let him go. Conduct your life with a happy heart, despite your trials. One day, I hope soon, he will see you and want to be with you again.
For now he needs to go.
I am saying this to you, and it is all very clear to me, but for me myself, I find it difficult to put into practice. My situation is similar to yours, and my advice to you is what I am trying to do, daily. Accept it. And wait patiently, while I live the best life I can.
M 43 S14 S13 D11 D7 Divorce final: Jan 2009 Making it up as I go....