If you can prove that you had a true common law marriage in the State of Texas, yes it is bigamy. You need to talk to a family law attorney in Houston Texas immediately. Her second marriage is not valid if she is still legally married to you.
Common law marriage is complex in Texas so you must talk to an attorney. You must be able to prove that a common law marriage exists. I assume that you want to file for divorce since she obviously no longer wants to be married to you.
Since bigamy is a crime. It is up to the District Attorney to prosecute her. Don't expect the DA to prosecute her. It is rarely done. You can take your evidence to the DA office and turn it over to them.
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