First, with regards XXXXX XXXXX money he owes you, you need to go back to the court that ordered support and file a Motion for Contempt against him. You can also go to the local Attorney General's Office Child Support Unit at http://maine.gov/ag/children_families/child_paternity_support.html to get the support and back support.
Second, as far as him turning you in, you techincally committed credit card fraud if you authorized an account with his name on it. However, as far as the money, if he sues you for the money, you can file a countersuit to offset the amount he owes you, but then you would be responsible (and still are responsible) for paying the credit card bill as it is not his. You should call the credit card company and seek to remove his name from the account and send them a letter stating that it is not his account and he is not responsible for the bill and you are the person solely liable for the bill. This should prevent any charges from being brought against you.
You should get an attorney to represent you and if you cannot afford one, contact the state bar and ask about the pro bono referral program.
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