In July 2010, Abby Ellin, a New York-based journalist, got engaged to a Navy doctor. He seemed exotic: He told her that he had worked undercover with the CIA and had made contact with Osama bin Laden. But Ellin soon grew suspicious. He gave her fake pearls that he claimed were high-end Mikimotos. She found out he was still trying to reconcile with his ex-wife. The Secret Service was watching him, he said. Her doubts mounting, Ellin, then 42, broke off the engagement.

More than a year later, on a blustery March day in 2012, the Naval Criminal Investigative Service (NCIS) called Ellin to tell her that the man — whom she nicknamed the Commander — had illegally prescribed Vicodin and other drugs. Ellin later discovered that he had a second ex-wife and was engaged to another woman while she was engaged to him. He had no CIA ties. He eventually served 21 months in prison.

In May 2015, Ellin published a cover story in Psychology Today in which she used her experience to explore how deception works. Her new book “Duped: Double Lives, False Identities, and the Con Man I Almost Married” looks even deeper into the subject. By telephone, Ellin (a friend and professional colleague of mine) talked about duplicity in her life — and ours:

(This interview has been edited for length and clarity.)

Q: As a journalist, weren’t you suspicious of the Commander’s rather grandiose-sounding personal history?

A: Of course I was — 8,000 percent. He told me that he’d treated Osama bin Laden when he was medical director at Guantanamo in the summer of 2009. He told me all these medical things that were wrong with bin Laden. I said, “This is just not possible. The president would have revealed that to the public.” And he said, “The president didn’t know.” And I said, “That’s nuts.” I even said, “That’s a stupid thing to tell a journalist.”

Eventually the journalist won out over the person who wanted to be in love.

Q: The Psychology Today cover story didn’t appear for more than four years after your breakup. Why the delay?

A: At first I was going to tell a story about being a journalist who was involved with someone who had a supersecret job. I thought maybe the story was about being someone who couldn’t figure out the facts. This was when I was still with him. And then immediately after I got the call from NCIS, I realized it was a different story. I decided to talk about others who have been deceived, to write about how do you deal with your life after something like this.

Q: What surprised you most in the course of your research?

A: I wasn’t quite prepared for how many people who had been deceived didn’t want me to use their real names. I thought, “Wow, this is something people are really embarrassed about.” It’s amazing how people don’t want to expose their perceived shortcomings. But if you marry a con artist, why should you be embarrassed? If you don’t know it until after the fact, it’s not your fault — other than the fact that you missed cues. There are often very good reasons.

Q: Women, you’ve found, tend to be less duplicitous than men.

A: Researchers at the Science Museum of London talked to 3,000 people and found that men tend to lie three times a day, whereas women lie about twice a day.

I think that’s in part because women haven’t had the opportunity to be as duplicitous, at least in the corporate world. And women do tend to suspend their disbelief more because we want to be partners. In that regard, men have a more receptive audience. Also, women tend to lie because they don’t want to hurt other people’s feelings, whereas men do it to puff themselves up.

Q: Were you surprised that the other women in the Commander’s life — “Kate,” his second ex-wife, and “Eileen,” to whom he was engaged while he was engaged to you — talked to you?

A: It was unexpected. Kate is a great, great mother. She wants to protect her children. She wanted to make clear that I wouldn’t use the Commander’s real name and out them. Eileen didn’t know what had happened. The Commander had just disappeared and left 26 bags of stuff in her garage. She was happy to talk to me because she was genuinely curious. I must say that he has great taste in women.

Q: What do you think might have happened had you had married the Commander?

A: Frankly, I could have gotten hurt. When I got the call from NCIS, I asked, “Could he get violent?” One night when we were together he was having nightmares about the “bad guys,” and started screaming and almost choked me. So I was worried. He’s out of jail and traveling, so I guess a part of me still worries about him blowing a gasket and hurting my family.

Q: After the Commander, you dated a painter who lied about being separated and was also seeing someone else. Do you attract an inordinate number of deceivers?

A: I have to take responsibility for this. I like people who are fun. I like people who are quick. I like people who have adventurous lives and aren’t everyday 9-to-5 people. In the past, I liked people who might not have been the best types.

But I’ve also talked with a lot of people and found so many who were either deceivers or had been duped. It wasn’t hard to find them. I met a guy who said that as soon as he was married, he knew he was going to cheat.

Q: You attended a workshop called “Spy the Lie,” devoted to spotting fakers. There are TED talks and videos on the subject. Is this a cottage industry?

A: I’m convinced this is a growing thing. There’s a real need for it. People really want this stuff. I think it’s really important, especially for women. I would like to start one of these initiatives myself.

Q: You say you don’t believe in happy endings. Why?

A: Because I’m hyper-aware of mortality. It used to freak me out when I was a kid, that we were all going to end up in the same place — in the ground, in the ocean.

Q: But isn’t the book a happy ending of a sort?

A: I guess. We’ll have to see how it gets reviewed.

Thomas Vinciguerra is the author of “Cast of Characters: Wolcott Gibbs, E.B. White, James Thurber, and the Golden Age of The New Yorker.”

DUPED

Double Lives, False Identities, and the Con Man I Almost Married

By Abby Ellin

PublicAffairs. 272 pp. $27.