Common law marriage is what most people mean by the Texas definition of an Informal Marriage; and it falls under the category of family law.
When two people wish to be married but do not apply for a license and have a formal ceremony they the law in Texas allows for them to have what is called an informal marriage.
Generally speaking, in order to have an informal marriage the following must exist:
1. a declaration of their marriage has been signed and filed with the County; or
2. the man and woman agreed to be married and after the agreement they lived together in this state as husband and wife and there represented to others that they were married.
Referring to #2 above this means the following:
1. There must be an agreement by both man and woman to be married
2. AFTER the agreement they must live together in Texas
3. AND they must represent to others in Texas that you are married.
The key things above are that you MUST live together in Texas AFTER you agree to be married. Also you must be able to prove that you have represented to others in Texas that you are husband and wife. If you cannot meet all three of the above, or if you did not file a declaration of marriage, then you cannot establish an informal marriage.