How can you tell if someone you just started dating will be your future spouse, or is just a few-month fling? Conventional wisdom and corny love stories tell us that the difference between “the one” and a short-term relationship is obvious.

But, according to a new study, it’s not so clear at first.

Research from the University of California, Davis shows that, in the beginning, long-term and short-term relationships are nearly indistinguishable.

The paper is published in the journal Experimental Psychology.

Surveying past relationships

Led by Paul Eastwick, an associate professor of psychology at UC Davis, the researchers conducted a survey of more than 800 people from various age groups.  

The researchers used a “relationship reconstruction” method in which they asked participants to recall specific experiences they had in their previous short-term and long-term relationships.

This differs from the traditional “relationship science” approach, which starts studying couples only after they started dating.

In this case, the participants had to reconstruct their relationships from the very beginning.

“Essentially, participants start by indicating which of a series of 50 events (e.g., first spent time together one on one, first kiss, first met his/her friends, first major disagreement) took place over the course of their entire relationship, and they assign actual dates to those events,” said Eastwick.

A surveying program then sorted out the dates in order, and participants were asked to state how positively they felt about the person during each point in time.

Levels of romantic interest

The researchers found that people reported similar levels of romantic interest in partners for both short-term and long-term relationships, and that this interest rose at the same level for both.

“The early events (e.g., first meet face-to-face, then flirt, then spend time together one-on-one) happen in the same average sequence in short-term and long-term relationships,” said Eastwick. “Only after some time do they diverge, at which point, romantic interest continues to rise in long-term relationships, and eventually, people start feeling attached to long-term partners.”

So, at a certain point, romantic interest tends to either plateau and decline, as seen in short-term relationships, or continue to rise until it develops into a long-term relationship.

But when does this happen, and why?

Usually, it’s when the relationship becomes sexual.

Sex and other factors  

“The moment at which long-term and short-term relationships tended to diverge was at about the time that people were having their first sexual experiences with the partner,” said Eastwick. “In other words, when you finally ‘hook up’ with someone, and there is sexual chemistry, you want that relationship to continue. When you finally ‘hook up’ and there isn’t sexual chemistry, those relationships tend not to last much longer.”

Until factors such as sexual chemistry and levels of support are determined in the relationship, it may be difficult for people to know where a relationship is going, he explained.

“I think this research points to some of the challenges inherent in predicting how long a relationship will last as people initially meet and get to know one another,” he said. “In the very early stages, it may be challenging for people to know exactly where a relationship is going until they have time to assess various predictors of compatibility.”

Conclusion

This study offers a unique twist to the common perception of a “sexy and exciting” short-term fling versus a long-term, stable relationship.

In reality, people may be in short-term relationships for sex even if they’re only slightly attracted to the person, while long-term relationships may be the ones that start particularly exciting and sexual.