Only a few states recognize common law marriages and each has its own requirements. If you live in one of those states and are actually common law married then it is the same as any other marriage and only a divorce can end it.
However, just filing a tax return is not being common law married there are usually many other requirements depending on the state. It would be tax fraud if not actually married to file a joint tax return. You might have a case against a tax firm that gave such advice.
If you think that you are, in fact, common law married then I suggest that you consult a family law attorney for help.
Un-doing such an "invalid" joint tax return is not simple and requires professional help since the IRS must declare the return invalid and then submit new single tax returns. You cannot simply amend to do that.
I suggest consulting a tax professional or tax attorney that is familuar with the procedure (not many are because it is rarely used and buried in the IRS manuals).
**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.**
