It seems every time I turn around I'm asked to pay half of some expense ie cost of tux for homecoming. My former spouse chooses not to work. In fact, more and more these days he's being given half of everything and then let completely off the hook for the complete financial responsibility of children. My ex is frequently late with child support but not enough to justify the expense of chasing him down. He doesn't have to pay a late fee or penalty while my checks are bouncing around town as a result.
Child support is based on basic needs and requirements for children.
I don't think a tux comes under this category.