Like marriage, divorce laws are determined by each of the 50 states, only nine of which -- in addition to the federal capital Washington -- so far allow couples of the same sex to wed.
"If a couple is living in New York City... they can get a divorce in New York City," said Sommer, who is Lambda Legal's director of constitutional litigation and senior counsel.
But complications arise when couples relocate to a state where their marriage is not legally recognized, said Stuart Gaffney, media director of the lobbying group Marriage Equality USA.
Thus, a couple living in Utah, where gay marriage is not recognized, can marry in Massachusetts, where it is legal and where newlyweds are not obliged to live in the state.
If the couple returns to Utah and their marriage falls apart, however, they would have to go to another state to petition for a divorce -- which requires a period of residence of six months to two years, depending on the state.
There are also local particularities. In Wyoming, for instance, same-sex couples cannot marry but they can seek a divorce.
"It's a mess," Sommer told AFP.
A Marriage Equality USA activist who requested anonymity to speak freely said such a situation left her in a state of stress and uncertainty as to how to legally and financial separate from her partner, whom she married in Canada.
"It made for a very difficult, untenable situation," she said.
"Within less than a year, after several years of uncertainty, we made the decision to end the relationship and begin the process of a divorce. I was very fortunate to be able to get divorced.
"Unfortunately, other US citizens who get married in Canada, or in other locations where same-sex marriage is legalized, rarely have this right," she said. "They are left in perpetual legal limbo.
According to the Williams Institute, which conducts research on the gay community, one percent of same-sex marriages -- of which there were about 50,000 in 2011 -- end in divorce every year, half the proportion for heterosexuals.
But even happily married couples who live in a state that recognizes gay marriage have to face "nightmare" complications, with divorce being the ultimate problem, Gaffney said.
That's because, under the Defense of Marriage Act, the federal government recognizes only straight marriages -- with hundreds of repercussions involving such areas as income tax and retirement benefits.
LGBT activists are thus eagerly awaiting how the US Supreme Court will rule on DOMA after its justices hear both sides of the legal argument on March 26-27.
"Non-gay couples are treated as what they are -- married -- no matter where they are living, traveling, or divorcing," said Evan Wolfson of Freedom to Marry, another group that campaigns for marriage equality.
"But gay couples experience a patchwork of respect, uncertainty and discrimination, depending on where they are," he said.
"That's why all couples should have -- the freedom to marry and divorce no matter where they live or find themselves."