Nicholas Sparks writes the equivalent of comfort food, high-carb, low-nutrition, but sometimes it hits the spot. His stories usually feature relationships that are not just true and deep and loving but healing. And then, like ripping off a band-aid, he tears it asunder, but in a manner that demonstrates just how true and deep and loving and healing the relationship was but how ennobling as well. And there is usually some object of deep metaphoric and sentimental value.

Ladies, prepare your hankies.

This time, the author of “The Notebook,” “Message in a Bottle,” “Nights in Rodanthe,” “A Walk to Remember” and this spring’s “The Last Song” (starring Miley Cyrus) gives us John (Channing Tatum) and Savannah (Amanda Seyfried of “Mamma Mia!” and “Big Love”). She is a kind-hearted girl and he is a special forces soldier with some anger issues. They have some soft-focus moments on the beach in Charleston while he is on leave and she is on spring vacation. She is considerate to his socially impaired father (Richard Jenkins) and he is understanding with her autistic neighbor. Two weeks later, they are very much in love, and agree to write as he completes his last year of service, as they look forward to being together as soon as it is over. But 9/11 changes everything. As Richard Lovelace wrote almost 400 years ago, “I could not love thee, dear, so much/Loved I not honor more.” As wrenching as it is for both of them, they know his place is with his team, defending freedom.

But then, she writes a “Dear John” letter telling him that she is engaged. He is wounded, recovers, and returns to battle. When he finally sees her again, he learns that her choice was not what he thought.

Director Lasse Hallström (“What’s Eating Gilbert Grape,” “The Cider House Rules,” “My Life as a Dog”) keeps things from getting too syrupy and Tatum and Seyfried have a sweet, easy connection. Henry Thomas (the kid from “E.T”) has warmth and humor as the single father of the autistic boy. Richard Jenkins does what he can in the underwritten role of John’s father, whose reserve and awkwardness may be attributable to an autism spectrum disorder. We’re on the side of these undeniably decent and very pretty people. But there is nothing they can do to make the last third of the film feel emotionally or narratively believable. If at the end of the movie, you ask whether there was any other reason for a character not to provide more information much earlier and the only answer is that they had to find a way to fill the last 40 minutes of screen time, that is not going to work. And the sweetness of the original connection is dissolved in what feels like a trick.