It does not cost much and you don't need a lawyer to file for divorce. I'd go down to the courthouse and do it right away. Filing will establish jurisdiction for the case and give you access to your parental rights as an individual.
You will need your own lawyer to resolve this. Divorces with children are complicated. Sharing a lawyer with you STBX is a no-no. Your second step should be to figure out how to get your own lawyer. Throwing your hands up and saying you can't afford won't cut it.