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First, I appreciate your vulnerability and honesty in your question. I truly think that acknowledging the problem is half of the solution. I would recommend, however, recruiting a real live Christian man in your life to hold you accountable. For all intents and purposes, I'm anonymous since you don't know me. Accountability goes a long way when you know someone will be asking you hard questions every time you see them. Draft 6-10 questions that will help you, and ask a mature Christian man in your life to ask you those hard questions on a regular basis (such as “Have you been mentally faithful to your wife?” and “Have you looked at pornography since the last time we met?” and “When was the last time you masturbated?”).
Second, I think you need to evaluate and eliminate the venue for pornography in your life. If you're looking on the internet, remove internet service from your home and/or get x3watch free monitoring (visit http://www.x3watch.com/). If you're getting on cable or satellite or other bonus TV, discontinue the service that provides those channels, and be honest with your wife about why you're doing it. If you're subscribing to magazines or video services, discontinue the subscriptions and ask your accountability partner to hold you accountable.
Finally, begin a rigorous discipline of memorizing Scripture. It is the single best thing you can do to see victory in this area, but it is hard work. Scripture memory not only assists in resisting temptation but it also re-programs the mind--and we men need both of those benefits! I don't think you are possessed by demons, per se. But it is very possible that you are being influenced by the demonic world. Scripture memory will help you battle the Evil One. Begin with Psalm 119:9-11; 1 Cor. 6:18-20; 1 Thess. 4:3; 1 Cor. 10:13; Job 31:1; Rom. 13:13-14; 1 John 1:9; Rom. 12:1-2; 2 Cor. 10:5; Matt. 5:27-28.
Hang in there. Pray. Confess when you fail. Pick yourself up again and ask the Lord for strength to resist temptation the next time. Don't get paralyzed by your guilt. Read James 4:7-10. Note that submission to God precedes resisting the Devil!