This form from Texas Law Help allows you to register your common law marriage with the county clerk. Texas law treats cohabitation agreements as binding contracts.Once signed, the declaration is valid proof of marriage and you are considered married for all legal purposes. How to Complete a Common Law Marriage Affidavit Form: The affidavit form is typically available online or from legal professionals. Here are a few documents that can be used to establish a common-law marriage. Affidavits. Filing for a domestic partnership in Austin, Texas, is an option to consider if you're in a committed relationship and don't want to marry. Learn about the importance of cohabitation agreements in Texas. Protect your assets and clarify ownership with this informative guide. It requires an affidavit of cohabitation if you have a roommate, but if like me, you don't, you have to submit an affidavit that you live alone. Consider reaching out to a Texas family law firm when drafting an agreement.