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By Melissa Dahl, NBC News

Sue and Bob Frause of Langely, Wash., have been happily married for 37 years. Or, as they might title the story of their lives: "Man, woman happily married for 37 years." 

One of their goofier common interests: the pair often slips into headline-speak, a result of their shared background in communication careers. (It's usually used to soften the edge of a request that might otherwise be considered naggy, explains Sue Frause. For example, she says, rather than calling her husband out for not doing the dishes, "I'll walk by the kitchen and go, 'Man leaves dishes in sink, woman throws pot out window' .... then and then he laughs and I laugh and it's not an issue.")

Sometimes it seems like a couple that's still in love after decades together actually is rare enough to warrant a news headline. Most of us assume that the sparks that fly during those dizzy, dreamy first days of a relationship fade with time. (Or, as Oscar Wilde phrased it: "One should always be in love; that is the reason one should never marry.") 

But that doesn't have to be the case, a growing number of studies are suggesting.

In a new national survey of married Americans, 40 percent of those who'd been married at least 10 years said they remained "very intensely" in love with their partner. The study sought to determine whether long-term romantic love was just a rare phenomenon, and the researchers, led by Daniel O'Leary, a clinical psychologist at Stony Brook University in Stony Brook, N.Y., were surprised to find just the opposite. Even for the longest marriages -- three decades or more -- 40 percent of women and 35 percent of men said they were still madly in love. 

The report, done by social psychologists at Stony Brook University and Harvey Mudd College, is already published online, and will appear in the March issue of the journal Social Psychological and Personality Science.

The report gathered data through a randomized telephone survey done over about four weeks in August and September of 2007, and the study results were drawn from the 274 married individuals across the U.S. who completed the survey. On average, the respondents were in their mid- to late-40s, and had been married for around 20 years. (A second survey was conducted in the fall of 2009, surveying just New York state residents. Just 33 percent of those living in New York state said they were still intensely in love with their long-term partners. But the researchers expected that -- those in the Northeast tend to report lower levels of happiness and well-being in general.)

They also wanted to find out some of the reasons why love sometimes does last for the long haul: Those who said they remained "intensely" in love were also more likely to think positively about their partner and to think about their partner when they were apart; they also reported more frequent hugs, kisses and, yes, sex. Lasting love was also associated with common interests -- especially those that were new or challenging -- and general life happiness. On the other hand, the results also identified two things that don't matter when it comes to long-term love: education level and money.

"The idea is we don't have to assume that it's just going to be serving the oatmeal to each other" as the decades slip by, says Arthur Aron, a social psychologist at Stony Brook University and one of the authors of this study.

Sue Frause, 61, says she and Bob, 66, believe intensity is good when it comes to love - but not when it comes to day to day issues that can get heated. They say one of the secrets to their relationship is that "we've learned to diffuse things that have become amplified so it's not that big of a deal," she says. "... It's got to be fun, otherwise, why bother?"

She says both of them strive to keep the romance alive, even in the simple things. He husband Bob, 66, recently made her a CD mix of love songs. For Valentine's Day, she's making him the same dinner she first made him when they were were dating. "I call it 'Sentimental Stroganoff'," she says.

Last January, Aron authored a study that looked at brain scans of adults in long-term marriages who said they still felt in love now as they had at the beginning of their relationship. They compared those images with brain scans of couples who had just fallen in love. The scans found similar activity in both types of couples in the ventral tegmental area, the reward-processing region of the brain. 

OK, but how do you make sure love sticks around? This may be that rare instance where advice found in women's magazines is right: Try something new together. You could take a class, start a new hobby or learn a new sport -- but it could be even simpler than that. Aron and his wife recently decided to do something together they hadn't done in years: hang out at a bar. 

And, as it turns out, you may be doing your part simply by reading this post. We assume that love can't last because that's what we hear again and again. But knowing that isn't always the case may be the first step to lasting love."There is actually a possibility that it's not just a fairy tale, that there are people that live happily ever after," Aron says. "Some people actually do it." contributor Diane Mapes contributed to this post.

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