What should I do about child support?

I’m filing for divorce from my husband of 16 years. He moved out 1 year and 5 months ago. During the first divorce hearing, the judge strongly recommended friend of the court for custody and child support. Since he left, I’ve have primary custody of the younger 4 and he’s had the oldest. The younger 4 goes to his apartment 2 days a week. My lawyer wants both of us to sit down and write out our expenses so we can come to an agreement for friend of the court. My ex sent me a list of his expenses and said he could only do $200 a month. I don’t know exactly what to do in this situation seeing how he is my only relationship. I do pay health insurance for all 5 kids and latch key for the younger 3 during school and my mom to be an au Pere during the week.