Did the L tell you that you have to file in order to get C/S? Or can you just get an order for C/S? If you do have to file, make sure everything else financial is separated too. You do not need to be financially responsible for any new debt he may create. You're very wise to protect yourself and the kids.
Life, I'm not saying this to be harsh, but your marriage was over when your H walked out the door. That said, it doesn't mean that at some point, well down the road, that you won't be able to build a new M with your H.
The faster you realize that MLC takes time, a lot of time in most cases, the better you'll be able to cope with what you have to deal with. Don't spend the time just waiting for your H to come out of the fog. Live your life for you and your children. Take this opportunity to work on yourself and be the person you want to be. A new world is open to you if you want to take the step.
It doesn't seem like it now, but you've been presented with a gift. What you do with it is up to you.
You're right, your H will most likely not fight for you at this time. It may not always be that way.
You're only done when you decide you're done. That's a choice you get to make.