The article below gets into great detail on what happens with pornography and the brain. There is also a link to a free e-book:

Hot Bods, the Bible and the Brain: The Truth About Porn Addiction

Along similar lines, this next article is written by Dr. Al Mohler regarding an article that J.R.R. Tolkien wrote to his son about sex and purity.

http://www.albertmohler.com/2014/03/11/from-father-to-son-j-r-r-tolkien-on-sex/

Have a good day in the Lord!