Your describing credit theft. It is fraud. It may be very simple to prove and if the defendant had any assets it would be worth pursuing the case. The problem is when you get a judgment can it be collected.?
You need to consult a bankruptcy attorney to review the facts with you. From what you have said it could be fraud, identity theft or your debt, it all depends on many more facts that a bankruptcy attorney can address for you.
Your ex-partner committed identity theft, which you should report to the police, and then dispute the negative credit information with the credit bureaus. Please see this FTC link: http://www.ftc.gov/bcp/edu/microsites/idtheft/
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.