"Erotic", in the subtitle, is a misnomer. Van Buskirk was a pedophile, though he seems not to have acted much on his desires. He was attracted, according to his diaries, to both young boys and girls. At least based on what we're given by the editor, he gives little description of any sexual encounter.
This book is fascinating in that it gives us a portrait of a disturbed individual. Despite the author's inexplicable attempts to portray Van Buskirk as normal, the diarist was not simply a product of his time. He was unable to keep a job and, on several occasions, absconded with others' money and possessions; when he joined the Confederate army, he deserted. He was obsessive, emotionally immature, and had sexual problems -- pedophilia, compulsive obsession and nocturnal emissions into his 30's. He was unable to maintain a meaningful relationship with any of the subjects of his quasi-sexual obsessions. Few memoirs give us such a window into the mind of a messed-up person.
Van Buskirk's diaries also provide information on life aboard US Navy ships in the mid-19th century, which was apparently characterized by frequent homoerotic behavior (which the obsessive Van Buskirk disapproved of but was fascinated with).