Either you are legally married or you are not. A common law marriage, if legal in your state, is as valid as any other marriage and can only be ended with a formal divorce. If you are not married then you need to correct any prior tax returns filed as married because they would be fraudulent returns.
If you are legally married then you must file married until divorced.
You might need the services of a family law attorney to work this out. Changing a prior joint return to single is not simple and usually requires a tax professional. It cannot just be amended, it must be declared a voided improper return by the IRS.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
