No. If you were not married on Dec 31 of the tax year, then you can't file a joint return. You'll each file an individual return with a status of "single". Then, if both of your names are on the deed and both of your names are on the loan, you can split everything right down the middle if you desire.
Usually what I see folks in your situation do is "take turns". For example, one person takes the property tax deduction and the other person takes the Mortgage Interest deduction. Then the next year they trade who takes which deduction.
