You may be able to file as Married Filing Jointly if you live in a state that recognizes common law marriage. Currently, the following jurisdictions recognize common law marriage:
Colorado
District of Columbia
Iowa
Kansas
Montana
New Hampshire
Oklahoma
Rhode Island
South Carolina
Texas
Utah
Living together in a common law state is usually insufficient - you need to hold yourself out as married including owning property together, having joint bank accounts, etc. To find out your state’s rules see:
http://family.findlaw.com/marriage/common-law-marriage-states.html
Alabama (2017), Georgia(1997), Idaho(1996), Ohio(Oct. 1991), and Pennsylvania(2005) are grandfathered for the marriages before the year indicated.
