In states that recognize common-law marriage (Wyoming is not one of them) holding yourselves out as married makes you "married" in that state. It's a "facts and circumstances" determination, and filing taxes jointly could be one circumstance that you considered yourselves as married. But if you did this in Wyoming, it was an incorrect filing and would not have any effect on your marital status.
Answered on Apr 20th, 2012 at 7:38 PM