I have read two short books on sexual purity recently. They are 'Sex is not the problem ... Lust is', by Joshua Harris and 'The Purity Principle', by Randy Alcorn. I would highly recommend both, although if I was to recommend just one of them I would tell you to read 'The Purity Principle.'
Interestingly they both give the following quote from John Piper:
The fire of lust's pleasures must be fought with the fire of God's pleasures. If we try to fight the fire of lust with prohibitions and threats alone - even the terrible warnings of Jesus - we will fail. We must fight it with a massive promise of superior happiness. We must swallow up the little flicker of lust's pleasure in the conflagration of holy satisfaction.