Question:
Answer:
First, from a purely legal standpoint, a common-law marriage is not the same thing as cohabiting. For example, a common-law marriage must meet certain standards of time lived together, and the couple must have the stated intention to marry, as well as hold themselves out to family and friends as being a married couple, such as through referring to each other as “husband” and “wife,” taking the same last name, and having joint back accounts or credit cards. By the way, most states do not either fully or even partially recognize common-law marriages at this point, apparently given what is otherwise available via legally recognized “domestic partnerships” in the modern world.
In either case, a person who wants to be baptized—whether strictly cohabiting or in a common-law marriage—would have to separate or get truly married. The only exception might be if the couple had children and the person desiring baptism agreed to live as brother and sister until such time as they would get married, and assuming their common-law spouse or “significant other” wouldn’t get married. But that’s a rather unlikely scenario, as a person unwilling to marry would not likely be willing to forego sexual intimacy. There could also be a case in which one or both people in the relationship would not be free to marry, given a prior marriage, and they could possibly stay together if they had children to raise. But they would have to live as brother and sister if they wanted to be baptized.
In any event, the Church makes clear that an adult be morally disposed to receive baptism:
Can. 865 §1. For an adult to be baptized, the person must have manifested the intention to receive baptism, have been instructed sufficiently about the truths of the faith and Christian obligations, and have been tested in the Christian life through the catechumenate.The adult is also to be urged to have sorrow for personal sins.
§2. An adult in danger of death can be baptized if, having some knowledge of the principal truths of the faith, the person has manifested in any way at all the intention to receive baptism and promises to observe the commandments of the Christian religion” (emphases added).