Difficult question to answer with the limited infomration provided. If the Court ordered counseling, through a Family Law Case, and if there is a prior court order that uninsured medical costs be equally divided, and if the child is still eligible for child support by way of the Court's order, it seems that at minimum you are responsible for 1/2 the costs.
If the court ordered you to pay for all of it, then that is the order.
If the court was silent on the issue of payment, then the order for payment cannot be enforced. However, a Judge was concerned enough about this child that counseling was ordered. If neither parent is willing to pay for this, that fact will be troubling to a Judge.
You need to review all the prior orders as well as the current order.
If there is no order for payment, you can go back to court and request an order.
Please note that this answer does not constitute legal advice, and should not be relied on, as each situation is fact specific, and it is not possible to evaluate a legal problem without a comprehensive consultation and review of all the facts and court pleadings filed in the case. This answer does not create an attorney-client relationship
Your question doesn't provide sufficient facts for me to provide a more comprehensive response than the following:
Your 18 year old is an adult, but for Child Support purposes, if you have a Child Support obligation it would continue beyond age 18 if your child is a full time high school student and not self-supporting, until the first to occur of your child completing the 12th grade or turning age 19. See Family Code Section 3901(a).
If you agreed to orders obligating you to support your child beyond the normal child support termination date, you would be bound by those orders. See Family Code Section 3901(b).
Family Code Section 3901(a) provides that the father and mother have an equal responsibility to maintain, to the extent of their ability, a child of whatever age who is incapacitated and without sufficient means.
If your child is incapacitated and without sufficient means, it is possible that the order for you to pay for your child's pysch counseling was intended to continue beyond the duration of your child support obligation.
If your child is not incapacitated, and the order for you to pay for your child's psych counseling was made before your child was 18 years old, it is possible that the order was intended to be in force only throughout the period of your court-ordered child support obligation.
However, you shouldn't bank on that possibility, because if the order was intended otherwise, you could face contempt proceedings as well as potential liability for harm suffered by your child as a result of lack of counseling.
If your court-ordered child support obligation has ended or is about to end, if you wish to terminate your obligation to pay for your child's psych counseling, you should file an Order to Show Cause or Notice of Motion for an order to terminate your obligation to pay for your child's psych counseling, if it is your desire to end that obligation.
However, you might consider your child's mental or emotional condition, your relationship with your child, and your desire and ability to asist your child, in determining whether you want to seek an order whose ultimate effect could be the termination of your child's psych ccounseling.