You do not file together with your fiance. Only legally married couples can file a joint return. If you were not legally married at the end of 2021 then you both file as Single. Or if there are children one of you might be able to file as Head of Household.
Am I Head of Household?
If you qualify as Head of Household, when you enter your filing status (single or married filing separately) into MyInfo, and then enter your qualifying dependent, TurboTax will offer HOH as your filing status.