You asked two questions.
Q1. The answer is no, child support is not tax deductible or reportable as income on an income tax return and it does not entitle the child-support payer to a deduction.
Q2. The IRS does not get involved in domestic relations. You may need a court order. Actually, you have a court order - your divorce decree. File your taxes and claim the dependent. When the IRS sends you the notice that someone has already claimed this dependent, respond with your court order showing you are entitled to the exemption. I am assuming that you have not negotiated any other tax-related terms for the dependent and that the right to claim the dependent was award to you in your divorce decree. If the decree is silent on the issue, then you must show that the child is your qualifying child and not the ex-spouse's. I suggest finding a reputable tax preparer or tax attorney in your area to help you with this situation.
DISCLAIMERâ€”This answer is for informational purposes only under the AVVO system, its terms and conditions. It is not intended as specific legal advice regarding your question. The answer could be different if all the facts were known. This answer does not establish an attorney client relationship. I am admitted only in Florida and Arizona.
First lesson, don't take tax advice from the non-custodial parent.
There is no income tax consequence with regard to child support to either the payor of the recipient. There is the question of the dependency exemption.
The IRS has a dependency test that would control the outcome of the dependency exemption claim in the absence of a court order that addresses the issue. Your disability would not decide the matter
You could choose to permit him to claim the exemption through an IRS Form 8332.
A situation frequently arises wherein the non-custodial parent realizes greater tax savings by taking the exemption than the other parent's increase tax liability for not taking the exemption. A frequent compromise is to switch the exemption and split the tax savings. That way both parents have a little more cash.