Texas recognizes informal or "common law" marriages. If you were to use a search engine, you would find Chapter 2 of the Texas Family Code. Subchapter E deals with "marriage without formalities" or a common law marriage. it the legal requirements are met, a common law marriage in Texas is just a valid as a formal marriage with a marriage license and a minister or judge performing the ceremony. A common law marriage creates the same duties, rights, and liabilities as a formal marriage.
To have a valid common law marriage, the parties may file a declaration and registration of informal marriage with a county clerk. This facilitates proof of the existence of the common law marriage should it ever be in question. If the parties do not use such a declaration, the common law marriage may be proved by (1) an agreement by the parties to be married, (b) after the agreement, they lived together as husband and wife in Texas, and (c) they represented to others they were married.
In my opinion, satisfying these requirements may be problematic. Both parties have to agree to be married - one party saying "we're married" won's suffice. Both parties must represent to others they are married. Just taking the word of one of the parties doesn't address the intent of the other. Both parties have to make the representation.
To prove the existence of a common law marriage after the parties have separated, a suit for divorce must be commenced within two years of the date of separation and ceasing to live together as husband and wife. If the suit for divorce is not commenced within that time, the law presumes the parties did not intend to be married.
Filing this suit for divorce in a common law marriage can be very important in the terms of division of a "marital estate" such as real property acquired during the marriage, retirement accrued during the common law marriage, and other investments and property acquired during the common law marriage. If the divorce is not filed within that two year period, dividing the estate will be much more difficult.