Bob Zielsdorf’s first letter to Fran Jordan was less than 150 words — much too long for a text message and certainly over the 140-character limit for a Tweet.

If social media had existed in the 1950s, perhaps the two eighth-graders from different states would have “liked” each other’s statuses on Facebook or shot off quick “I <3 you” texts — “I love you” in text speak — between classes instead of developing an 8-year relationship through handwritten letters that resulted in a 49-year marriage, five children and 10 grandchildren.

In “Sealed With a Kiss: An American Love Story in Letters” (Two Shores Books, $14.99), the former Sidney and Springfield resident shares the letters he and Fran exchanged from the time they first met in 1957 to their wedding in 1965. Available on Amazon in trade paperback and Kindle editions, the book hit No. 1 in its category (Family & Childhood Biographies) on its Jan. 22 launch date.

“It’s just so great for our family,” Fran Zielsdorf said. “When I read the book, it was like going back to that time and having it happen twice.”

They met when Bob Zielsdorf, who spent about six years of his childhood in Springfield in the late 1940s and early 1950s, got permission from his parents to travel alone by train from his home in York, Pa., to Andover, Mass., to visit a friend. There, he met Fran, and the two shared an innocent kiss over a game of “Spin the Bottle” during an outdoor party with his friend’s buddies. They exchanged addresses at the end of Bob’s trip, and when he returned to York, he decided to send Fran a letter.

She wrote back. And he wrote her again, and she wrote back. Pen pals at first, their letters contained lighthearted banter about school activities, friends, favorite songs and other bits of pop culture, such as a new TV show Fran liked called “American Bandstand.”

“It’s just the greatest,” she wrote. “Do you watch it? If you don’t, you really should.”

As time passed, friendship turned into love, although the two still conducted the majority of their relationship through letters, sometimes going three years without seeing each other. Bob moved to Milwaukee, spent time in France and attended college at the University of Notre Dame, while Fran attended Lake Erie College, in Painesville, Ohio, near Cleveland, and studied abroad in Spain.

They’d eventually exchange close to 500 letters by their wedding date — with Zielsdorf joking that he had to marry Fran as quickly as possible because the price of stamps kept increasing.

“We had no idea until we got married that we both had kept all the letters,” he said. “They’re a neat picture of life in that era.”

Before retiring to Vero Beach, Fla., in 2008, Zielsdorf was the longtime owner and CEO of The Peerless Group in Sidney.

As he looked over all the letters, notes, Valentine’s Day cards and other correspondence he and Fran shared — complete with the original envelopes with postmarked stamps — Zielsdorf wanted to preserve the memories of his courtship by writing a book. He took a memoir-writing class at the Vero Beach Museum of Art in 2009, and met a local writer, Suzanne Fox, who worked as a consulting editor and marketer for the finished, self-published work.

The Zielsdorfs are as much in love as they were when they won each other’s hearts through letters more than 50 years ago, and say their willingness to compromise, admit wrongs and remain committed to their union has kept their marriage going strong.

“It’s an old cliché, but we never went to sleep angry at each other,” Zielsdorf said.