Alone in his room, Harry was trying to think of a way to get ahold of a copy. His first idea was to perhaps borrow one from one of the girls, but that would involve actually talking to the girls. This was something Harry just wasn't comfortable with. In fact, the only girls he was ever comfortable talking with were Hermione and Ginny.
Sometimes people left books laying around the common room, so Harry thought that maybe he'd get lucky and someone would leave a copy, but no, the girls seemed rather protective of their book, and nobody ever left one laying around.
Harry knew this wasn't the sort of book he could ask his father for. Mum would of course find out that he had asked for it, and would want to know why. Then an idea began to grow in his mind. There was someone who could get it for him, someone who was like a parent, but without all the awkward questions.
He quickly scribbled a note to Sirius and sent it off with Hedwig.
A few days later, Hedwig returned with a large bundle and a letter from Sirius. Harry couldn't wait for the day's classes to end so he could finally satisfy his curiosity. As soon as supper was finished, he raced upstairs and began to read.
As he got into the first book, his eyes grew wide. He had figured it was something spicy, but had no idea how much. With each chapter, Harry's face grew warm and his pajama bottoms became uncomfortably tight. He rubbed himself through the fabric, trying to relive some of the tension.
The more he read over the next few days, the more addicted he became. It was extremely hard to tear his attention away from the book and go to class. One day, Harry decided to sneak the book into Snape's class. On that particular day, class was rather boring. Snape was droning on about some dark creature that Harry had no particular interest in. When Snape seemed to be preoccupied with something, and his attention was away from Harry, Harry pulled out the book and hid it inside his D.A.D.A. text and began to read.
Once again, that exquisitely painful tightening in his trousers occurred. Ever so quietly, Harry slipped a hand underneath his desk so he could rub himself. He was so engrossed in pleasuring himself that he never heard the footsteps coming up behind him.
"Detention Mr. Potter. My office. Tomorrow evening." Snape purred in his ear.
With that final stimulation, Harry came in his pants and had to go to his next class all sticky.