What your going through is really tough, and really common. I have some theological advice for you, and some practical advice.
Firstly, on a theological level. The guilt you feel over what you are doing is normal, and its right to feel guilty for sin. However, at the same time you need to keep in mind the message of the gospel - that Jesus Christ has paid completely for all of your sin. Romans 8 begins:
“Therefore there is no condemnation for those who are in Christ Jesus. For the law of th Spirit of life has set you free in Christ Jesus from the law of sin and death. God has done what the law, weakened by the flesh, could not do. By sending his own son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but the Spirit.” (Rom 8:1-4)
It’s a long quote, but its worth a close look. There are several things to point out from it:
1) We can never make ourselves righteous, that is to say, we can never be good enough for God. The law - God’s rules for good living - is incapable of making us righteous because we can never live up to it (cf. Gal 3:10-14).
2) Even though the law was ‘weakened’ by sin, God has made us righteous. God has completely paid for your sin in Christ - there is now “no condemnation” if you believe that Jesus has died for your sin, to make you righteous before God (cf. Rom 3:20-26).
3) Now that we are ‘in Christ Jesus’ - that is, now that we have come to believe that he has paid for our sin, God sends his Spirit to help us to live the way he wants - ‘to walk according to the Spirit’ (cf. Rom 6:1-14).
This doesn’t mean that we are going to be perfect. Unfortunately, the Bible’s picture of sin is that we are enslaved to it, and helpless to rescue ourselves (eg. Eph 2:1-3). Even when we become Christians, we are not rid of it completely but are encouraged to fight against it. The truth is that internet pornography is probably something that you are going to have to battle with your whole life long. However, the gospel means that we are not helpless in our struggle (Eph 2:4-10). While ever we live this side of heaven, we strive (imperfectly) to ‘put on Christ’ (Rom 13:14), to ‘walk in the Spirit’. But, here’s the big BUT… as we strive to ‘put on Christ’, and live good lives, we do so with confidence that even when we screw up, God still accepts us. Even if we screw up “seventy times seven” (Matt 18:21-22), Jesus death is enough to pay for our sin. Satan will always try to make you feel like its not, and make you doubt your salvation, (eg. Zech 3:1, 1 Pet 5:8). But the victory is yours because it is God’s victory and “there is no condemnation”. God will always accept you because of Jesus. You should find comfort in that, and confidence to ‘boldly approach the throne of grace so that you might find mercy in your time of need’ (Heb 4:16).
Secondly, on a practical level. We men always have to watch our own godliness, especially on the internet. There are systems that you can put in place to help you in this. Where I study, at Moore Theological College, we all use an accountability system. We have a program called “Covenant Eyes” (http://www.covenanteyes.com/) which monitors everything your computer downloads and sends a report to a friend (of your choosing) so that your friend can keep you accountable. Find a godly man that you can trust, if you are married then you may ask your wife, and ask that person to pray for you, and check up on you. Obviously this is going to have to be somebody you know well and trust. It can be nerve wracking to ask someone to do this for you, but you would be surprised how much less tempting dodgy sites on the internet might become if you know that someone will ask you about what you were doing.
Hope that helps, Trey.