Message in a Bottle by Nicholas Sparks

During her morning jog on the beach, journalist Theresa Osborne discovers a bottle protruding from the sand. Inside it, she finds a heartbreaking, anonymous love letter. After her paper publishes the letter, Osborne tracks down the letter's reclusive author, world-weary widower Garret Blake in the Carolinas. But, as Osborne finds herself falling hopelessly in love with Blake, she becomes wracked with guilt over the real impetus for her visit.