British researchers are reaching across the pond to find American couples -- gay or straight -- who have experienced love that has endured.
The Open University of Great Britain is looking for adults in long-term relationships to answer a confidential online survey about what their love means today.
The surveys from the Enduring Love Project will eventually be compiled into a book. So far, 4,000 Britons have responded.
"Quite simply, we want to find out what couples do that allows relationships to last, that lets them succeed in that most challenging of tasks -- continuing to love," said Susan Quilliam, editor of the revised "Joy of Sex," and one of the researchers.
"There's been nothing done so far that's been as in-depth or far reaching -- and as well as being academically significant," she said. "Enduring Love will be hugely useful for society and for ordinary folk."
The study will not presuppose that "such relationships are uniformly loving or straightforwardly associated with contentment," said the Enduring Love Project's outline statement.
Rather, it will look at things that help people sustain relationships and "how cultural myths, such as finding 'the one' and living 'happily-ever-after,' are understood and reconciled by adult couples whose own relationships may fall short of these romantic ideals."
With a half of all marriages in the United States ending in divorce, enduring love is "rare," according to Gail Theon, a licensed psychologist from Plymouth, Minn., who specializes in the needs of baby boomers.
But those that do last, rely on trust.
"Right at the top of the list for these couples is trust, even beyond sexual trust, which is part of that," she said. "Basically, the person behaves in a way that is consistent with your mutual values."
"You must have 100 percent loyalty and love, either in an erotic or an enduring sense," she said. "When you are always anxious about the other person, it takes away from the joy of love."
Couples whose relationships are enduring have a shared sense of humor and mutual respect, she said. Sex, but more importantly, intimacy, is also critical.
"Freud would tell us from a classical sense, it's all about sex, life and death," said Thoen.
Not everyone can have sexual intercourse, especially as they age, but there are "modern interventions."
Other elements that can make or break a long-time relationship are communication and money, she said.
"There are shared commitments they have to live up to," Thoen said.
"I still think there are a lot of silently unhappy people," she added. "Statistics can be very misleading, especially in this economy and uneasy world. Unfortunately, a lot of desperately unhappy people are married."
But Phyllis Koch-Sheras, a Virginia psychologist and co-author of the 2012 book, "Lifelong Love," said couples can learn how to have enduring love.
"All of us can change," she said.
Her book, written with her husband of 35 years, psychologist Peter Sheras, examines the "four steps to creating and maintaining an extraordinary relationship": commitment, cooperation, communication and community.
"It's not a commitment to each other or an individual, but a commitment to the relationship as an entity," said Koch-Sheras. "Instead of thinking about just meeting your own needs ... you keep working together to create something you haven't thought of before that serves to support the couple."
Communication "seems obvious," she said. "But too often therapists teach the skills too early and the couples end up using communication to criticize and blame and beat up on each other. Then we have couples who say, 'Yup, that convinces me, I'm out of here.'"
She recommends a "proclamation mission statement" that helps the couple define what is important to them.
"We recommend you change it every few months," said Koch-Sheras. "The couple is always creating, not creative."
Finding support from other couples -- community -- is also important, she said.
"Have a way to connect with other couples in positive relationships," she said. "It takes a village to raise a child and to keep a couple alive and growing."