So first thing. Call and get an appointment with a lawyer. Ask around for referrals and see if anyone knows of one who's handled a divorce with complicated financial matters. Most of them have a 1-hour free consult so you can at least go in and ask some questions and get a feel for who/how the lawyer is. A lawyer is probably going to recommend a forensic accountant...and that can get very expensive, so be prepared. You may qualify for legal aid if you don't work...but it takes time to apply, so you're at risk there.

Second thing, scour the house and find any documentation you can find about what was in the account, account numbers, etc. If the account was set-up through his employer, he has a history of paycheck deductions...so you'll be able to show how much was being deducted each month.

Next, stop obsessing over your ex. He clearly doesn't give a crap about you. If he did, he wouldn't be trying to leave you penniless and destitute. You shouldn't have relied on him for money in the first place...but now that you did and you know he is about to try to leave you to starve, you should be worrying about that...not him. My advice is that you get a job...because the divorce process is long and expensive. So you need to have access to cash...either from family members or employment.

And lastly, have a backup plan. You're about to embark on a long, messy divorce process with complicated financial matters. So you need to be prepared for the worst case scenario which is that the money is gone. If it is, what are you going to do? Prepare for the worse and hope for the best. That way you're covered no matter what happens.
What would you have done with your life if you weren't waiting around for Prince Charming to financially fund your adulthood? That's the question you need to ask yourself and start doing that.

Its such a shame so many women are in your position. I'm not sure when women are going to get the message of how amazing it is to have the pride of self-reliance but it can't happen fast enough. If you have girl children, I hope you're teaching them to get educated and employed so they don't end up in your situation.