The general rule is that you can't claim a deduction for something you didn't pay. You can split the mortgage deductions 50/50 if they were paid out of a joint account. Otherwise, technically you should divide according to who paid what.
Once you're married, this won't be an issue if you file a joint return.
Remember, the only deductible expenses on a personal residence are mortgage interest, property taxes, mortgage insurance (PMI), and points. Other closing costs are not deductible.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
