If you live with someone for over seven years are you considered "legally" married to that person?

Some states will consider your relationship a "common law" marriage, but not all.

Well I don't think that's how it works

In all the states that I knew of as having a common law marriage law did away with it quite a few years ago. Check with an attorney in your area or tell us what state you are in.

Heterosexual couples can become legally married without a license or ceremony. This type of marriage is a "common law marriage". It was to be believed that, a common law marriage was created when two people simply live together for a certain number of years. In order to have a valid common law marriage, the couple must do all of the following:

1. Live together for a significant period (not defined in any state)
2. Hold themselves out as a married couple (typically this means using the same last name, referring to the other as "my husband" or "my wife," and filing a joint tax return)
3. Intend to be married.
When a common law marriage exists, the spouses receive the same legal treatment given to a formally married couples, up and to include the requirement that they go through a legal divorce to end the marriage.

Common Law marrieages have been abolished in most all states.

Common Law Marriage FAQ (http://www.nolo.com/article.cfm/objectId/709FAEE4-ABEA-4E17-BA34836388313A3C/catID/3C3AF4CE-DB9E-48C4-8DFCFE2E47C91747/118/304/145/FAQ/)

Most states do not reconise common law marriage in the US any longer

In at least one
States to have a common law you have to go to the court clerk and register your common law marriage for it to be reconsied

If you live with someone for over seven years are you considered "legally" married to that person?
I know in New York... There is no common law marriages but I'm not sure about other states

Common law marriage also known as “informal marriage” or in legal terms, “marriage by habit and reputeis", is recognized only in the following states:

Alabama
Colorado
District of Columbia
Georgia (if created before 1/1/97)
Idaho (if created before 1/1/96)
Iowa
Kansas
Montana
New Hampshire (for inheritance purposes only)
Ohio (if created before 10/10/91)
Oklahoma
Pennsylvania (if created before 1/1/05)
Rhode Island
South Carolina
Texas
Utah

Each state has different legal aspects to the law that should be examined.