No, you still have to pay child support. In addition, for the sake of discussion, you could not just decide to stop paying child support, only a Court Order ending your obligation would allow you to stop paying child support. The fact that he is going to get SSI has nothing to do with your support obligations. From the facts you state, it seems he is incapable of living on his own.
Leonard R. Boyer, Esq. 201-.675-.5577. Please be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.