1. Go find an attorney who specializes in family (divorce) law in your former state. Act now.
2. Have your attorney send her a demand letter on your behalf stating that she must return your funds immediately. In that letter, be sure to specify the origin of every dollar in that account. For example, $20,000 of severance pay. $3,000 from sale of your baseball card collection. $4,000 deposited each month from your payroll over the past two years. Make it clear that the money is yours and you expect to get it back.
(this letter won't do you much good now, BTW, but it might help you later on in court when you assert your rights to the money you earned)
3. Have your attorney file for divorce within the next two weeks.
That's about it. Seriously. Time to stop pu$$yfooting around and take steps to protect your long-term ability to provide for your kids' well-being.