I have the same situation, counting the days between paydays, checking my account all the time.
My ex won't pay cm, there us no point asking for anything because it comes with too much emotional manipulation and threats.
I've even had to take a laptop to the lawn shop to make ends meet and the constant fear if loosing my job because of all the things that go on looking after the DDS, managing school, childcare, and my over compensations for the shit my ex left us in, at times, feels overwhelming.
Worst is people who are not in this situation just don't get it.
I wish I could balance by budget but stuff just keeps on cropping up.
So etines I feel that it's better not to have family or my ex to ask for help because of the emotiobal debt along with the financial debt.
I do believe that one day it will be better and we'll get over this. God only knows when that will happen.
So I do get how you feel, I don't have much of an answer to help or guide you to get through this, other than try to keep on top of it and don't let it break you (sorry that's easier said than done).