A few ideas.
You two could use marital counseling. However, if she has her mind made up that she's 100% done, you can still go alone
. Get some emotional tools as to how to deal with things.
I would also contact an attorney or at least a mediator if I were you. Protect your rights in terms of finances and custody/visitation. If she sees it as a hostile act, then so be it. You have rights and shouldn't just roll over on them, no matter how you're feeling. You sound like a caring guy and your children certainly need you. You can work out a lot via mediation but there should be written documentation when it comes to schedules and money. Getting your ducks lined up does not have to, 100% of the time, lead to a divorce. Still, protect yourself and your kids.
And finally, I hope you are under a doctor's care. You sound depressed (I am not a doctor), and it's possible you've been that way for quite a while. No matter what, it can't hurt to get checked out if you haven't been recently, at least for your own peace of mind.
Hang in there.