Still responsible for paying off ex’s debt forgiveness?

Filed/completed a dissolution of marriage the end of 2025 and I was planning to file taxes for this past year as an individual as I thought you were supposed to file as the status you’re ended the year as. My ex says we’ll get a bigger return if we file as married still, and that’ll be okay since we were married 10/12 months of the year. He also said it’s ideal as I wouldn’t get any tax return anyway because it would be absorbed by the IRS given he had a debt forgiveness payment plan with them since before we got married: when we got married as he was a 1099 employee for a long time prior, through 2023 (we first filed jointly for 2022). My name was on the payment plan and I believe still is. I didn’t work or have taxable income for almost the whole time we were married so all of that debt is from *his* 1099 filings. Is this all true? I feel like he’s using my new high paying job as leverage to pay off his residual debt. TIA.