Oh no, don't let him get away with changing the bank passwords. Tell him he either puts it back to something you know or you are going to a lawyer - and then DO IT. Either that, or march down to the bank in person and take out half the money. (My H pulled that too - twice - and changed them back when I threw a hissy fit.)
I don't think it is a coincidence that this is the second time my H wanted to leave - the first was when our DD was about 9 months old, and he says this time he started thinking about leaving when S was 9 months old. Too focused on the baby, not focused enough on H.
I'm fairly confident my H is in a pseudo-EA - he confessed that he considers a woman at work his "best friend", and for a man who needs conversation/friendship/companionship as much as him, that is A Very Bad Thing. He doesn't think he did anything wrong. I do. I sent her an email (and copied her fiance) calling her a homewrecker - H was soooo angry that he filed for divorce as soon as the lawyer's office opened the next morning (after 7 weeks of threatening to file).
We were definitely in a power struggle for years, both of us too insecure to tell the other what we were concerned about, and both of us feeling the other was "controlling".
One of my mantras is "It's not my responsibility to take care of H. He can take care of himself." I'm not very good at this yet, but I'm working on it. About a month into the situation was when I started to have stronger moments, and that's about when the anger stepped in. Now, two months in, I'm up to half-a-day of feeling really good at a time, and I'm not angry as often. You can do this.
