Any bride will tell you—at great length—how stressful it is to plan a wedding. But what about the guests? Rarely does anyone acknowledge their pain.

As this summer’s wedding season heats up, my stateside pals tell me they're counting on cinematic comic relief: They have high hopes for the July movie Wedding Crashers, featuring Vince Vaughn and Owen Wilson as randy rogues who prey on starry-eyed bridesmaids at their most susceptible. I can sympathize.

Even here in Britain, the country that produced Four Weddings and a Funeral, that wry, candid classic of champagne-fueled hookups and heartbreak, we haven’t mastered the art of attending O.P.N.’s (Other People’s Nuptials).

Every year there are around 2.2 million weddings in the United States, and roughly 300,000 weddings here in the U.K. Multiply that by the length of the average guest list—about 200, in both countries—to get a sense of just how many of us go through the familiar routine: pick main course, pick present, pick outfit, pick date. If you’re in a serious relationship, the last choice is already made for you, but you can still find yourself picking—at each other.

The truth is that these lovely, sacred events—opportunities for voyeuristic romance and, hopefully, some amour of your own—often wreak havoc on relationships that are, shall we say, at the tipping point. Is it the sight of another couple making the ultimate commitment? The "are you two next?" factor? The sense that your friends are moving forward with their lives, and you’re in a holding pattern?

In Jackie and Neil's case, it was the groom's speech. Jackie, a 26-year-old advertising executive from West London, remembers, "He said that when he had first seen his wife he thought, 'Wow!'. I realized that I didn’t go, 'Wow!', when I first saw Neil, and had always felt that he was the one who was more into me."

Although she and Neil had been seeing each other for four years and living together for one, Jackie knew things hadn't been right for a while. She admits, "I'd already started worrying, and was looking forward to the party side rather than the romantic side of going to the wedding."

The death knell sounded when Jackie overheard the mother of the bride urge Neil to "get a ring on that girl’s finger." She called it quits the very next day.

Family weddings can up the ante even more. Jennie, a doctor who lives in Devon, and Martin*, a Royal Air Force pilot, had been together for four years when Martin’s brother got married. At the event, "I was being considered part of his family," Jennie remembers. "I felt as if I could be married to Martin already, which felt very scary."