!!!!!!!!!!
That's what you need a lawyer for, hon! Maybe you can just say you're sorry, but you can't consider mediation as long as he is asking for 100% percent custody of the kids. That will give him something to think about (he'd have to cough up more $$$ to file another motion if he agrees to change it). Tell him you can't agree to anything right now without running it by your lawyer first, and that if his motion remains in its current form, you will be forced to counter it.

Maybe this will buy you some time. You can let your L know you don't want the divorce, and that you're only acting to protect yourself and your kids. It's to your advantage that you're in a fault state (I'm in 50/50 Texas).