If your filing status is Married Filing Separately, you must itemize if he itemizes. If he itemizes and you take the standard deduction, you will receive an IRS notice down the road.
Business expenses are not itemized deductions. If your soon-to-be ex has a home office, its possible that he is writing-off some of the home expenses on his business schedule. That would leave less of the mortgage interest and taxes for itemized deductions.
Obviously, the amount of these expenses matter. In some parts of the country, property taxes are more than others. If you live where these costs are high (and definitely higher than $6300), you should be prepared to itemize.