Maia Leppo didn’t think that she and her boyfriend, Alex Kobzik, had a problem until they were vacationing with his family on Cape Cod, Mass., last summer, eight years into their relationship, and his mother asked them when they had first said “I love you.”

They managed to stammer through the conversation without telling her the truth: They still hadn’t said it. Although they shared a car, bank accounts and an apartment, talked openly about the future and generally expressed how much they cared for each other, they had never used those specific words.

Even out of earshot of Mr. Kobzik’s mother later that night, they didn’t address the issue. “We didn’t talk about it at all,” Ms. Leppo said. “At that point I was like, ‘This is ridiculous.’ ”

A few weeks later, she heard a request on the radio program “This American Life” that seemed tailored for her predicament. The talk show was seeking volunteers who had a personal message that they wanted help delivering.