The question is considerably more complicated than that.
The Constitution is silent on the subject of marriage, which means that the definition of marriage falls to the state government. In Massachusetts, the state constitution was sufficiently unambiguously worded that the state supreme court found that denying marriage to same-sex couples was in violation of the state constitution. In other states, the state constitutions are not written in the same way, and so the matter would be decided differently. And in a significant number of states, the constitutions have been amended to prohibit gay marriage.
Further, there are two issues. (1) Will the state license people to perform same-sex marriages, and recognize those that are performed in that state? (2) Will the state recognize same-sex marriages that are performed in other states?
(1) is entirely a matter of the state’s constitution and laws. The Federal government cannot force a state to define marriage in a particular way, because the precise definition of marriage is up to the state.
(The question of Loving v Virginia was whether the Lovings should be prosecuted for miscegenation; the Supreme Court found that that was a violation of due process and equal protection, and served no public good. So Virginia could not prosecute two men who were married in Massachusetts unless it can show some public good that is served, but it is not forced to marry two men.)
(2) is the one that requires resolution at the federal level, and it is the main reason that the word marriage is so important. The Constitution requires states to give “full faith and credit” to contracts and obligations executed in other states—which requires that two men who are married in Massachusetts be treated as married by Utah, or Florida, or Texas. This one is the slam-dunk, legally speaking.
What I expect we’ll see over the next 10 to 15 years is that same-sex couples will come to Massachusetts to get married in increasing numbers, and sooner or later there will be a state that treats a married couple as unmarried, and the case will go to the Supreme Court. Once that happens, provided the justices rule according to the Constitution, the other states will fall like dominos, because there’s no benefit in banning gay marriage when people can take a bus to one of the states where it is performed, get married, return home, and expect the state to recognize it.