It's not yet clear whether people who are already jealous or heartbroken are more likely to engage in this kind of Facebook surveillance or if being an active Facebook user directly causes those feelings.
But other studies contribute to the possibility that excessive social media use can cause romantic harm. One study, published in 2011, found that undergraduates who spent so much time on Facebook that it intruded on their relationships reported being more dissatisfied in those relationships. Partners can end up feeling neglected, ignored, and concerned about why the people they're with seem more excited about their virtual lives than their real ones.
After surveying about 200 people, researchers reported last year in the journal Cyberpsychology, Behavior and Social Networking that the most active Facebook users experienced the greatest number of Facebook-related conflicts -- such as adding former romantic partners as friends or spending too time on Facebook at the expense of time together.
And people who reported the most Facebook-related conflicts were more likely to end up cheating, breaking up or getting divorced. The findings only held for people who had been together for three years or less, suggesting that new relationships are the most vulnerable to Facebook intrusions.
The same group of researchers recently reported similar results in the same journal after surveying of more than 500 Twitter users. People who were more active on Twitter reported more Twitter-related conflicts and more negative relationship outcomes as a result.
"It's kind of like the old adage that if you do anything too much it's going to have implications," said Russell Clayton, of the University of Missouri, Columbia, who co-authored both studies. "I personally think Facebook and Twitter are great. But if you are experiencing Twitter-related conflict, you should probably reduce the amount of time you spend on it."
Marshall also urged privacy and cautiousness.
"Be careful what you post on Facebook and Twitter and if you are concerned about something coming back to haunt you, err on the side of not writing anything at all," she said. "And don't fall into the trap of digging around for information about your ex-partners. It can be very addictive. Just leave it."