James 4 verse 7: submit to God, resist the devil, and he shall flee from you.
Romans 8 verses 1 and 2: Therefore, there is now no condemnation for those who are in Christ Jesus, because through Christ Jesus the law of the Spirit of life has set me free from the law of sin and death.
When the enemy tempts you to watch pornography, or commit any other sin for that matter, there are weapons that God has given you to fight back. A simple prayer like 'I plead the blood of Jesus against this temptation.' is enough and it will work. When you repented of your sin and gave your heart to Jesus, he broke all hold that your sin had on you. You are no longer of the world, and therefore no longer under the authority of the devil. You are now under the authority of Jesus. At the cross, Jesus took our sins so that we might have his righteousness. When you submit toHim you can wield His authority over worldly powers. Most Christians who struggle with recurring sins/confess cycles simply haven't realised this awesome truth yet. I know I didn't when it came to my recurring sins, smoking, alcohol and substance abuse, sexual immorality and video games. Then I realised that God wasn't in heaven going 'tsk tsk tsk, look at Dan screwing up again'. What he was really saying was 'Dan why have you gone and taken off those pure white robes I gave you and traded them for some grotty old thing you found in the trash can? You don't have to wear that any more, you aren't that person anymore, why don't you go and get back into your royal robes?'.
How's this for a prayer. Say aloud (must be aloud, the devil and his minions can put thoughts into your head but he CANNOT read your mind. God alone can do that.) 'I submit to Jesus and command all of His enemies to leave my presence immediately.' Guess what? If you do this every demon or spirit that is not of God MUST IMMEDIATELY leave you alone. Our God is so great that he helps us to fight those spiritual powers that would attack us.
Remember that Satan has no power over you save that of deception. He can make you believe lies. You say you are addicted to pornography? Before you came to Christ you were correct. Now though, as those verses in Romans state, you are free from sin. It has no place in your life. We all sin because we are not perfect, and we shall not be perfect this side of glory, however God's word is truth and His word says you are free from sin.
God also says that in Christ you are the salt and light of the Earth(Matthew 5:13,14), that you are a branch of the true vine, channel of His life(John 15:1,5), that you have been chosen and appointed by God to bear fruit(John 15:16), that you are a personal witnesof Christ(Acts 1:8), that you are a temple of God(1 corinthians 3:16), that you are a minister of reconciliation for God(2 Corinthians 5:17-21), that you are God's fellow worker(2 Corinthians 6:1), that you are seated with Christ in the heavenly realms(ephesians 2:6), that you are God's workmanship, created for goodworks(Ephesians 2:10), that you can approach God with freedom and confidence(Ephesians 3:12), that you can do all things through Christ who strengthens you(Phillipians 4:13), that you are free from condemnation forever(Romans 8:1,2), you are assured that all things work together for your good(Romans 8:28), that you are free from any condemning charges against you(8:31-34), that you CANNOT (by anything,ever) be separated from the love of God(Romans 8:35-39), that you have been established, anointed and sealed by God(2 Corinthians 1:21,22), that you can have confidence that the good work God has begun in you shall be perfected(Phillipians 1:6), that you are a citizen of heaven(Philippians 3:20), that you are hidden with Christ in God(Collossians 3:3), that you have not been given a spirit of fear, but of love, power and self discipline(2 Timothy 1:7), that you can find grace and mercy to help in time of need(Hebrews 4:16), that you are born of God, and the evil one cannot touch you(1 John 5:18), that you are God's child(John 1:12), that you are Christ's friend(John15:15), that you have been justified(Romans 5:1), that you are united witht the Lord and share one Spirit with Him(1 Corinthians 6:17), that you have been bought with a price and belong to God(1 Corinthians 6:19,20), that you are a member of Christ's body(1 Corinthians 12:27), that you are a saint, a holy one(Ephesians 1:10), that you have been adopted as God's child(Ephesians 1:5), that you have direct access to God through the Holy Spirit(Ephesians 2:18), that you have been redeemed AND forgiven of ALL your sins(Collossians 1:14) and that YOU(yes, you reading this) are complete in Christ(Collossians 2:10).
This is the stuff that God says about you. Choose to belive Him instead.
All my love in Christ
Dan