If you are both equally responsible for the debt, but he paid the mortgage, then he would put the deduction on his taxes. However, the tax laws have changed considerably so many taxpayers are no longer able to itemize their deductions because the standard deduction amount has increased significantly.
New Standard Deduction Rates:
Single - $12,000
Head of Household - $18,000
Married filing Joint - $24,000
So mortgage interest and property taxes, and other itemized expenses must be greater than those amounts to itemize. You can see a some key components of the tax changes in the link below.
Key Tax Reform Changes for 2018