There is no such 7 year rule that exists anywhere in the United States. In most states, common law marriage is not recognized at all. According to the National Conference of State Legislatures, only 9 states now recognize common law marriages formed within their borders: Alabama, Colorado, Kansas, Rhode Island, South Carolina, Iowa, Montana, Oklahoma, and Texas plus the District of Columbia. There are 5 states that have grandfather clauses recognizing common law marriages that were formed before a certain date: Georgia, Idaho, Ohio, Oklahoma and Pennsylvania. In Pennsylvania, where I practice law, common law marriages can only be recognized as valid if formed before January 1, 2005. New Hampshire only recognizes common law marriages for probate purposes. Utah only recognizes common law marriages which have been validated by a court or administrative order.
So how does one get into a common law marriage, assuming one is in a state that recognizes it in some way. It requires more than the mere fact of a couple living together. There must also be a mutual agreement and intent to be married such as by the two people at some point saying to each other that they are married AND, they must also present themselves to the outside world and conduct themselves as a married couple. Such acts would include introducing each other to others as their husband/wife; filing tax returns as a married couple; establishing joint ownership of property, bank accounts and other assets; using the same last name. It is not required that a couple do all of these things. Rather, if a court is determining this, it would look at all the circumstances and facts as a whole.
Now while a common law marriage can be created without a wedding, to end it requires a divorce just as with a marriage begun with a formal wedding ceremony.
In my experience, the issue of whether a common law marriage exists or existed is most likely to come up in one of two contexts: divorce or death.
In a divorce, there are rights to distribution of marital property which can award one spouse assets even if his or her name is not on the title due to the broad powers given to the courts in such matters. If there is no marriage certificate, before one can obtain the rights inherent in a divorce, it would be required to prove that a marriage existed in the first place.
In the case of a death, spouses have certain rights of inheritance. If a person dies with no Will, in Pennsylvania, the spouse will be entitled to at least one-half of the estate or more depending upon whether the deceased had children. If the deceased made a will but left the spouse nothing, the spouse can elect against the Will and claim one-third of the estate. In the absence of a ceremonial wedding, there could be a dispute as to whether a common law marriage existed.
It should be no surprise that judges strongly dislike common law marriage. It creates disputes and ambiguity and adds to the court's docket. In Pennsylvania, for years, judges were urging the legislature to abolish common law marriage. Finally, in 2004, the legislature passed, and Governor Rendell signed, a bill that provided that beginning on January 1, 2005, no new common law marriages could be formed in Pennsylvania. Those that existed before that date could still be recognized so the courts will still have to deal with such cases for some time.