https://coag.gov/resources/frequently-asked-questions/colorado-office-attorney-general-frequently-asked-questions
A common-law marriage in Colorado is valid for all purposes, the same as a ceremonial marriage. Only death or divorce can terminate it. The common-law elements of a valid marriage are that the couples
(1) are free to contract a valid ceremonial marriage, i.e., they are not already married to someone else; (2) hold themselves out as husband and wife; (3) consent to the marriage; (4) live together; and (5) have the reputation in the community as being married. The single most important element under the common law was the mutual consent of a couple presently to be husband and wife. All the rest were considered evidence of this consent or exchange of promises. No time requirement exists other than the time necessary to establish these circumstances. When proof of common law marriage is required, such as by an insurance company, a signed affidavit can be presented. A sample affidavit is presented here
https://coag.gov/sites/default/files/contentuploads/ago/FAQ/OAG/common_law_sample_affidavit.pdf.
Common-law marriage is a term used to describe a marriage that has not complied with the statutory requirements most states have enacted as necessary for a ceremonial marriage. The name came from the fact that these marriages were recognized as valid under the common law of England. In 1877, the United States Supreme Court stated, in an action that questioned the validity of a non ceremonial marriage, that marriages that were valid under common law were still valid unless the state passed a statute specifically forbidding them. Meisher v. Moore, 96 U.S. 76 (1877). Since the Colorado legislature has never enacted such a statute, Colorado is part of the minority of states that recognize the validity of common-law marriages.
If you desire a legal opinion relating to a specific situation, you should consult your own attorney.