You are in a very precarious position. Why are you waiting for the sky to fall?
I see that you are scared H will leave and stop paying bills, leave you with no place to go.
This is within your power to change. Find out exactly how much child support and figure out what you need to live, you and S.
If you cannot support you and S, if H wants custody, that will not be in your favour.
Sell some stuff, talk to a lawyer to find out EXACTLY what your options are.
Maybe an option would have to be moving back home. S is fifteen and I realize he has developmental delays and I know Kids on the AS don't respond well to change, but things are going to change anyway..they already have,
You are a strong, wonderful mother and person.you can indeed do this.
