ANSWER:
First, as a married person, you have the absolute legal right to elect to file a tax return separate from your spouse. (And if you qualify, you may be able to file as "head of household.")

Second, if you file a “married filing separately” your spouse must do likewise. He cannot file as an unmarried person.

Third, if you file a “married filing separately” and itemize deductions, your spouse must do likewise. He cannot claim a standard deduction.

Fourth, while itemized deductions may be “split” between married spouses filing separate returns (for example, you deduct half of the home mortgage interest and he deducts the other half)/ But both spouses cannot claim the full amount of any specific single deduction.

Since you apparently filed first, your return is accepted by IRS as being true, accurate, correct, and in compliance with IRS rules. As has apparently already occurred, IRS will reject the husband’s return

Further discussion:
If your filing status is married filing separately, you typically report on your income tax return only your own income, expenses, credits, and deductions. Therefore, if you paid for a doctor's appointment out of your separate checking account, you would claim that deduction on your return. Any medical expenses paid out of a joint checking account in which you and your spouse have the same interest are considered to have been paid equally by each of you, unless you can show otherwise. Different rules may apply in community property states (such as California.).

Each spouse may be able to claim itemized deductions on a married filing separate return for certain expenses that are either paid separately or jointly with the other spouse.

If the deductible expenses that are paid out of separate funds, such as medical expenses or employee business expenses, they are deductible by the spouse who pays them.

If the mortgage payment and property taxes are paid through a joint account they be shared equally on the Schedule A of the respective Spouses tax return. (So you should claim only one-half on your separate return.)

Sometimes the deductible expenses that are paid from community funds, the allocation of the deductions may depend on whether or not you live in a community property state. In a community property state, the deduction is shared equally between both of the spouses.

Finally, you would be well-advised to make copies of the mortgage and property tax information and furnish the copies to your soon-2BX. If you do not do so, he will be able to eventually compel you to do so under court order. And if the mortgage and property taxes were actually paid through the use of joint funds, you might consider filing an amended return so as to claim only half the amounts rather than the entire amounts. Even better, for both spouses, is to now join with husband and the two of you now file a joint return. (Generally, married filing separately puts one or the other taxpayer, and often both, in the worst of all tax positions. Filing a amend return jointly with spouse may very well result in a tax saving for BOTH spouses. Better to kept the money (and split the savings between the two of you) rather than giving the money to Uncle Sam.

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