The requirement for a partner visa (820 visa) is to be in a de facto relationship or married, or have your relationship registered, to an Australia citizen, Australian permanent resident or an eligible New Zealand citizen. The applicant must also be lawfully in Australia when they apply for the subclass 820 (i.e. on a substantive visa or bridging visa). You must have been in your de facto relationship for twelve months or longer prior to the application. You must be in an exclusive relationship to the exclusion of all others.
Note: For the subclass 309 partner visa, you must be outside of Australia when applying and when the visa is determined.