He was the biggest egomaniac I ever fell in love with. A stunning singer/songwriter in his sexual prime, Dave made fun of fat girls, carried a baseball bat in his car in case of trouble, and called my dear grandfather “Gramps” the first time he met him. He wore skirts in public just for the attention, and had me write his college entrance essay because hallucinogens had stymied his powers of concentration.

The last words he said to me were, “What, do you want me to treat you like a princess?” I figured anyone who couldn’t puzzle that out was destined for failure in life.

But an ill-advised Internet search last month revealed that Narcissistic Acid-Head Dave is now … um … Dr. Dave, a heroic veterinarian who brings beasties back from the brink of death. An online newsletter lauds my ex-beau for saving Dewey, a Chihuahua foster puppy, by securing “little bone screws” on the mutt’s “tiny leg.” Further research revealed Dave lives with 18 pets and an astonishingly beautiful wife who clearly has no princess complex but (thank you, Google) does have a warrant out for her arrest.

All this cyber sleuthing was inspired by Five Men Who Broke My Heart, Susan Shapiro’s nonfiction account of tracking down her greatest loves. My book club agreed to read the tell-all, then dig up dirt on our own former flames. I found the exercise addictive, dredging up ex-lovers’ marriage licenses and wedding photos, charting their careers and offspring, spotting lies on their résumés and misspellings on their Web sites.

Thanks to Google, Classmates, Facebook, MySpace, and LinkedIn, you can now find almost anyone online — instantaneously and anonymously. But what you find is sometimes shocking.

A fellow book club member hunted down the nicest boy she ever dated, a Cornell architecture student. “I can’t tell you how white-bread sweet he was,” she said. These days, he’s a dreadlocked, highly pierced tattoo artist who won TLC’s Tattoo Wars. Another found that her “low-life” boyfriend, who worked at the I.V. co-op, is now a successful patent attorney.

“The guy I lusted after in high school?” said another friend. “Fat and bald.”

The revelations aren’t just fun — they’re emotionally stirring.

“It makes you think about what your life would have been like if you stayed with that person,” explained another friend of mine.

You may find yourself searching for clues in his life that he never really got over you: Did he marry someone who looks like you, or name his kids what you always said you’d name them? And you can’t help wondering — just for that one ugly moment — how he managed to accomplish any of this without you.

But why should we care what these also-rans are up to?

“Revenge? Comparison?” offers a friend. “I mean, I’m glad I’m not with him, but I’m even gladder if he doesn’t own half of New York City or have pictures of him on his 200-foot yacht on his MySpace page. You know what I mean?”

Another gal said she finds comfort in seeing evidence of life-after-breakup. “It’s a way to revise history,” she said, “to prove it wasn’t that bad after all. See? Everyone recovered.”

If you decide to cyber snoop on a paramour, be prepared: A surprising number of them turn out to be gay. I can’t explain this. It’s just a thing.

And keep your peeping in the digital arena. “There’s no harm in looking online,” said a friend, “but if it goes beyond virtual and into actual reality, you’ve crossed over into bunny-boiling territory.”

But that’s nothing Dr. Dave couldn’t handle.