First, as a married couple, you need to be filing your taxes as Married Filing Jointly or Married Filing Separately.
If you were legally married on December 31, 2018, neither of you should be filing as Single.
When filing jointly, you will both pay the credit.
If you continue to file separately, either of the homeowners can pay the credit.
For more information, follow this link: https://www.irs.gov/newsroom/first-time-homebuyer-credit
