Vampire Diaries Stefan's Diaries The Complete Collection Books 1 - 6 Box Set by L. J. Smith (Origins, Bloodlust, Craving, Ripper, Asylum & Compelled)

Stefan Salvatore fell in love with a girl right before he fell in love with Katherine and the girl's name was Cheyenne Hall. She had curly blonde hair and she wore glasses. Her eyes were blue. Presumably ever since Stefan learned how to write, he had been writing in diaries a majority of his life after that. Often writing down memories, facts and reminders in order not to forget them. In one particular page he kept a photograph of his ex-girlfriend, Katherine Pierce. When she actually read one of the diaries with her photograph in it, she asked him "You came back to fall in love with me all over again, didn't you?". She also mentioned that one diary included all of his inner thoughts and feelings.
In The End of the Affair, we get to see one page of Stefan's diary - March 12, 1922. We also get to hear Elena reading selections from 1922, 1924 and 1935.
In For Whom the Bell Tolls, Stefan burns the majority of his diaries as a result of his memories being erased by Qetsiyah when she performed a spell that linked him to Silas, which "fried" his brain.