When can I stop it and how
You cannot just stop paying child support. You must file a motion with the Court to have him declared emancipated and have the court order payments to cease. You should retain counsel to handle this correctly.
Without meeting with you, and knowing all the facts and circumstances of your case, my opinion is not to be construed as legal advice, just general educational information.
As previously indicated, to officially terminate your child support obligation you must secure an Order directing that the child is emancipated and that your child support obigation is terminated upon a set date. If you ex will cooperate, you can acheive this by filing a Consent Order. If your ex will not cooperate you must file a Motion with the court requesting such relief.
Kenneth A. White, Esq.
The Answer provided was based on the limited information provided, and represents information based on the law in general, not a legal opinion that can be relied upon. Before a formal legal opinion can be offered I would need an opportunity to review all possible relevant facts and circumstances. You cannot rely on the advice of an attorney given over the internet. The exact facts of your sitaution, including facts which you have not mentioned in your question, may completely change the opinion that is being offered. Please be aware that the above comments are neither protected by attorney-client privilege, nor may the same be the basis for a malpractice lawsuit.