Nicholas Sparks’s best-selling love stories (and the movies based on them) are often set in North Carolina, not Boston. But the author considers our fair city to be one of the more romantic places on the map. “We had one of our really fun pre-wedding events there,’’ said Sparks, whose wife is from Manchester, N.H. “We took our 10th anniversary trip to Boston.’’ Sparks will be back in the area on Sunday when he signs copies of his latest book, “The Best of Me,’’ at 2 p.m. at the Harvard Coop. Sparks, who checked in by phone from Charlotte, apologized in advance for the fact that he will be signing copies of only the new book, nothing else. He said that if he agreed to sign anything brought to him, he’d be at the Coop all night putting his signature all over paperbacks and DVDs, including “The Notebook,’’ which starred Ryan Gosling.