My husband a male had established a domestic partnership with women. They lived together in Florida and Texas for about 2 years.

My husband a male had established a domestic partnership with women. They lived together in Florida and Texas for about 2 years. She did not use his last name, but they filed their Federal Income Tax together for the year 2007 and she was also added to his health insurance as a dependent.
I think they are considered married or at least have an established “Common Law Marriage”, thus making my marriage to him void and not legal. Please advise

Current resident of Tennessee, married in Texas

How do I get a copy of the Federal Tax return? How do I get a copy of the insurance papers where he added her to his policy?