Between the two of you, you can only claim the total amount of interest and taxes paid during the year. If he already claimed the full amount, then taking an extra deduction will get one or both of you in trouble.
Typically, you can claim the part you actually paid. If you lived together until October and earned about the same as your spouse then a fair claim might be 1/2 x 10/12 = 41.67% of the total. However, if you are audited and the IRS detects that you and your spouse together claimed more than the total, they can go after either one of you or both of you. You have to decide whether or not to take the risk.
Ideally, this issue would be covered as part of your financial settlement in any divorce or separation order. You might ask for an adjustment in your favor for the amount the deduction would have saved you if it had been split fairly.
