@purpletmgmt-gmai
An important part of recovery is accountability, but that goes both ways. Bringing your ex’s deception to the attention of the IRS is not punishment or vindictiveness, it is holding her accountable for her own bad choices.
I also very strongly disagree with @fanfare . The IRS has three years to audit any tax return, six years in the case of a problem that causes a greater than 25% difference in the amount of tax due, and the IRS can audit a taxpayer essentially forever if they accuse the taxpayer of civil fraud. On any joint tax return, both signatories can be held jointly and severally liable for any errors on the tax return. For that reason, I believe it is vitally important that you inform the IRS that you were not married for those years, and that you did not consent to filing a joint return. It is true that if you only care about the stimulus check, you only need to file a 2020 tax return. But the entire situation is a mess and no one can predict how or when it might turn on you in the future.
Good luck.
