"Them" refers to Peter's brother, Ben Alden, and his fiancee, Marissa Evans. When Ben and Evans, both 31, started dating three and a half years ago, the brothers were sharing an apartment in New York City. "Peter wasn't about to let his best friend go," Evans says, so "he made a great transition from wingman to third wheel."
In Peter's Instagram shots, he shamelessly photo-bombs the couple all over the place, from intruding on a Facetime conversation to appearing as a fuzzy figure amid the bushes during a professional photo shoot. In eight months, Peter has amassed more than 75,000 followers, with commenters sharing their own third-wheel stories and asking to appear as guest couples.
But being a couple's sidekick hasn't always been glamorous. Take, for example, Jeff Kinney's series Diary of a Wimpy Kid, where one book follows the romantic exploits of sixth-grader Greg as he attempts to snag a date for his school's Valentine's dance. His plans go horribly, and he is left alone while his best friend Rowley marches into the sunset with the girl of his dreams.
Kinney says he tried to capture a kid's initial feeling of "betrayal" when his childhood friend chooses a love interest over him. "You feel broken up with," the writer says.
"You've put a ton of time into this friendship, you think you know them better than anybody else, and suddenly they're changing into a different person." While that pain might be most potent for teens, it's similar to watching a best friend get married, Kinney adds.
Anna Goldfarb dealt with the pain by blogging about it. Two years ago, Goldfarb, now 36, was single and fed up with making plans with her girlfriends, only to have their significant others tag along.
"I'm starting to think that I was the front wheel of a tricycle in a former life," she wrote on her dating blog Shmitten Kitten, lamenting moments when she had to trail behind a couple or sit alone while they cuddled during a movie.
Now that she's in a relationship herself, Goldfarb says she would never make her single friends feel left out. "It's the aspartame version of a friendship," she practically spits. "I have no tolerance for it. I will shut it down."
Though some might ask their friends for more one-on-one time to help cure the third-wheel blues, Goldfarb thinks that can be even more awkward: Your friend might conclude that you dislike their significant other and get defensive. "I would rather dye my hair and move to another country than actually confront a friend about this," she says.
Little academic research has been done on third-wheeling. But Brian Ogolsky, a human development professor who studies romantic relationships at the University of Illinois at Urbana-Champaign, sees advantages to being on the sidelines of a happy couple.
"We derive our expectations in relationships from those around us," Ogolsky says. "So if we see positive role models, like a peer couple in a healthy relationship, we're likely to pick up behaviors to use in the long run."
Peter Alden says he'll be ready for a relationship eventually. "When I meet the right person, I'll know," he says, "and she'll be the fourth wheel." He pauses. "Assuming that my brother and Marissa approve."
