If your divorce was not finalized until 2020 then for the 2019 tax return you must either file as Married Filing Jointly or Married Filing Separately. You cannot file as Head of Household since you were both living together at some time in the last six months of the year. Payment of medical expenses is not support so is not entered on your tax return as income.
See if you can agree to file as Married Filing Jointly and if receiving a tax refund consider splitting the refund 50/50 or in some way that satisfies both parties. Filing as MFJ is almost always the best way to file when married, otherwise you are going to lose some tax credits or have other credit cut in half if you file as MFS. And if you live in a community property state it can get complex if you file separately.
See this TurboTax support FAQ for filing jointly versus separately - https://ttlc.intuit.com/community/married/help/is-it-better-for-a-married-couple-to-file-jointly-or-...
See this TurboTax support FAQ for Head of Household when married - https://ttlc.intuit.com/community/married/help/can-a-married-person-claim-head-of-household-filing-s...
