My son has turned 18 as of April - he has not completed high school - was expelled the last 2 years. I have had no contact with him due to his mother for the past 16 years so I cannot say if he will be attending school again or not in the fall or if it will be full-time - I do know he is still living with his mother. I have requested that my child support obligation end due to the circumstance but my ex-wife has decline which means I'm still paying. Is there anything else I can do other than go to court since I really can't afford it?

No, you need to read your child support order that is in place, what does it say ? If you merely talk to your attorney he may say just stop paying if the court order says you can stop. Of course the ex wife will say keep paying, that is the last person to ask.

My child support order states the payments will continue as long as the child is "a child of the marriage" per the divorce act. Of course my ex-wife has already said the payments still should continue - she is not willing to terminate the payments.

Huh? I've never heard of a child support agreement like that. Such agreements will state until the child has reach x age, or until they have finished their education.

I've never hear of such an open ended deal. What state are you in? Have you tried checking what that phrase "child of the marriage" means? Did you have an attorney to assist in the divorce?

Unless you can point to something in the divorce agreement that justifies ceasing support, then you will have to continue paying.

Talk to a lawyer. Most states follow the rule that if a child is over 18 and no longer in school, the child support ceases. It will cost you less to pay a lawyer to file for a modification of support/cessation of support than to keep giving your ex wife pocket money.

I live in Ontario, Canada.
A child of the marriage means as long as the child resides with the mother or parent full-time and is under the age of 18.
I'm a bit worried that my ex-wife will want the payments to keep coming as long as she enrolls him in school.
I'm going to contact a lawyer this week to find out where I stand on this.
Don't get me wrong, I don't mind paying as long as my child stays in school full-time and gets a good education. But I also think if I'm forced to go to court the judge might rule in her favour saying that I need to continue with the payments to give him a chance to graduate... how many chances does he get?!