Marriage is about a lot more than falling in love. Marriage is also a legal and economic relationship which, among other things, provides spouses with important property rights when they divorce. In Minnesota, a divorcing spouse has the right to an equitable share of the couple's marital property. An unmarried person living with his or her significant other generally has no similar right to property division when the couple breaks up.
A few states - not including Minnesota - recognize common-law marriage, in which a marriage is deemed to exist even if the couple never went through the formalities of a marriage certificate and a wedding ceremony. A common-law marriage is typically proved by showing the couple lived together, consider themselves a married couple, and hold themselves out to others as a married couple. In states that recognize common-law marriage, the parties have the full property-division rights of spouses in a formal marriage.
As cohabitation without marriage has become more socially acceptable, common-law marriage is increasingly becoming an historical relic. The increase in unmarried couples living together has led a few jurisdictions to grant some marriage-like protections to partners in a cohabiting relationship when they split up.
Minnesota is not one of those jurisdictions. Here, an unmarried couple who live together in a sexual relationship have no rights in each other's property unless both parties sign a written contract to that effect. Such a contract is enforceable only after the parties break up. Under Minnesota law, in the absence of such a contract the state courts have no jurisdiction to enforce a claim by one former cohabiting party to the property or earnings of the other.
Source: National Public Radio, "No, You're Not In A Common-Law Marriage After 7 Years Together," Heidi Glenn, Sept. 4, 2016