I know this is tough but I have to agree - tell him nothing.
I am certainly not an attny but having been wrapped up in the nightmare that is NY state legal system for 18 months I really learned the importance of two things (1) Patience (2) KEEPING MY MOUTH SHUT.
I don't know what state you are in or what the divorce laws are but if it's a joint checking account then I would think (again, I could be way off base) that you are entitled to at least 50% off that account no matter if you use it or not. If your name is on it, it's half yours. As I see it you *are* paying for your legal fees.
It doesn't matter if your H has the money or not. He can get a loan, a second job, have his wages garnished or work out a payment plan with the firm you choose. NOT YOUR PROBLEM!
I know you just want to grab him and shake the crap out of him (been there) but you have such a position of power here and the best way to use it is to give him NO INFO!