This is why the Federal Judiciary and especially the Supreme Court is so damned important. Marriage has traditionally fallen under Article IV, Section I - The Full Faith & Credit Clause. In other words, if one state recognizes or codifies your marriage, all the other states are bound to recognize the marriage as well.
This is not the first time that this was an issue for marriage and the Full Faith and Credit Clause. Back near the turn of last century, Utah was facing the possibility of being stripped of it's statehood if they didn't get a handle on the polygamist marriages. Utah bowed to pressure, as did the Mormon church, all because other states didn't want to recognize polygamist marriages.
When enough states recognize homosexual marriage, it's only a matter of time until people in other states sue in Federal court under Art. IV, Sec. I, and they'll start winning. DOMA will be challenged and ultimately, like most things that are contentious social issues, will be solved at the Supreme Court. If something happens to one of our four justices before the next GOP president, homosexual marriage will certainly become the law of the land.
...and in the eyes of the dems/libs...it'll be "settled" law....exempt from ever being overturned, which is what they've demanded with the Roe v. Wade..."settled once and for all."
It's a repeat like in the days of Noah, except for water we'll get fire.