What should I do about this?

Need some advice on what you’d do if you were in this situation. My son is 12 years old, and we’ve never had a court order but our agreement was always Mom Sunday 5 pm to Thursday Morning then dad got him after school to Sunday at 5 pm. No child support was ever provided even though dad made sufficiently more then mom. Covid happened, and I was basically given Thursdays as well. fast forward to this September I got a new job and could no longer drive my son to school so he started going to dads Monday after school until Friday. Dad has never done any driving for school, extracurricular activities, etc. has only provided needs for when he is there. Fast forward to now, our son needs braces and the dad wants to split 50/50 while mom financially can not afford to. What would you do? Go after child support and use that money towards braces or have your child suffer from not being able to afford them? Dad can afford them but refuses to foot the bill himself.