We bought a house: should we file our taxes separately or get married and file them together?

My partner and I just moved from Washington state and bought a house in Texas. He's paying for the down payment while I pay for closing costs, appliances, and furniture for the house. We didn't think about our taxes until after we submitted our loan application that listed our marital status as "unmarried". 

 

Will we get the biggest return if we file separately? Or should we get married by the end of the year to file jointly? If we do file separately, who legally can claim the property taxes on their tax return?

 

Other things to note:

  • I make about 2x more than he does
  • His job is hourly and my job is salary
  • I've started to list our marital status as "married" on insurance policies and utilities, but wasn't sure if that would be enough to considered common-law married in Texas so that we could file jointly