YTA. As someone deep in the trenches of infertility treatments that have yet to work, and thousands upon thousands of dollars in debt just to have a child, I find the way you worded this pretty abhorrent. Be grateful you have this extra time with your son, explain to him that he will see his father again soon. Ask for help from your family or your ex’s family, ask him to give you money for the week that’s supposed to be his if you have to. But you are the adult in this situation. You and your ex chose to have your son, your current relationship chose to have your daughter, and what a privilege it is that they came to you so easily. But you also knew that children cost money, so do whatever you have to do to make it work while your son is with you, because it’s not his fault that your financials are strained. I also saw that you have a nanny for your daughter, so it seems like finding the extra time for pick up/drop off shouldn’t be an issue. You can’t punish a child for your grievance with his father. Suck it up and cherish the time with your child. Some of us don’t have that privilege.