You've had a lot of good advice why. I've been in a similar position so I've got a few things to say too.
He is being financially abusive by systemically shutting you out of online bank accounts, controlling all the money, refusing reasonable requests for money and insisting you're crap with money.
The first thing you need to do is open your own bank account. Do this asap. This will start your credit rating again.
Next apply for child benefit. This is a must. Child benefit is the basis of other benefits should you need them. Get this paid into your new account.
Get yourself onto his account, the one that he gives you the card.
Find any documentation that he had other assets and copy them.hide these copies away or give them to a friend for safekeeping. Include passports with this.
As you have the children and he will have other assets in his name eg savings, pension, you will not have to split the house 50/50. Particularly if the children stay with you most of the time you are entitled to a larger chunk of the house.
If you want to go into nursing there is an NHS bursary that will help you. It has a generous childcare allowance too. I'm on a similar course and I do not have fees to pay and am managing on this + other benefits + maintenance. Check out if theres any uni nursing fees though first.
You will also be able to claim free school meals, council tax reduction, child tax credit and the winter fuel allowance. It all adds up. But you must have child benefit first.
It's you do feel that your marriage is over, and can contain your feelings for a little while (not for everyone, its hard) then its worth making you and your children financially secure.