Ex and I separated in October of 2024, having had joint finances from Jan-Sep 2024. Come tax season, we file married but separate, she finds out her withholding rate was too low and she owes over a grand in back taxes. Ex reaches out to me, and asks me to contribute half of 70% (9 months of joint financials) since we had both spent jointly from our shared account. I disagreed that I should be held liable for her back taxes, since I paid my portion of taxes, and as of 12/31/24, we were no longer supporting each other financially or sharing any responsibilities as partners in any capacity due to having separated. She is essentially asking me to pay back half of what 70% of her back taxes would be, since I jointly spent from that account during that time. Am I in the wrong here?