First of all, very few states still recognize common-law marriages and secondly, even common law states (as they are called) have requirements that must be met before a partnership will be considered a legal marriage. Living together for an extended period of time is certainly one of those requirements but in addition, the parties must typically hold themselves out as a married couple. This means that you and your partner consistently introduce yourselves as Mr. & Mrs., file joint tax returns, etc. just as a married couple would do.
In short, states do not just “declare” that a couple is married when they have had no intention of forming such a union.
That said, it is possible (and quite common) for unmarried couples to discover that they have created a partnership of sorts that requires legal intervention to divide. This often happens when couples have cohabitated for a long period of time and have accumulated joint assets and joint debts. In this instance, the couple may still have to go through a property distribution trial or mediation to divide the property when the relationship ends.
For this reason, it’s a smart idea to draft a cohabitation agreement so that you and your partner are clear as to how you will deal with property and assets if the relationship should end in the future.
For more information on drafting a cohabitation agreement, read the helpful book I Do, You Do, But Just Sign Here.