Talk to an attorney immediately, just to have a plan in place in case things turn for the worst.
Also, watch your money and any joint account(s) the two of you may have together. Your new goal is to protect yourself and your children, as much as you can, from the inevitable storm you are all going to have to weather together. But, after all is said and done, you'll come through it on the other side better off. If someone doesn't want to be married anymore, you can't force them to stay married. Become a business partner with her, and your business is raising your children.
Hang in there, and if it helps you to pray, pray as much as you can. But don't forget to protect yourself (and your family) down here as well. Sounds like you did a pretty good Plan A, and if you need to move to a Plan B, have everything ready to go.
I hope things work out for you. Keep your head up and stay strong for your kids.