The core of your problem is the pornography. You are filling your mind with images that are not proper for a Christian to be thinking about. Then you use those images as a focus for sexual lust. If you are going to serve Christ, you have to exercise self-control. Though Paul was talking to married couples, the general concept remains true, Satan has an open door to "tempt you because of your lack of self-control" (I Corinthians 7:5). "For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God" (I Thessalonians 4:3-5). But you have been using "passion of lust" (pornography) just like those who have no respect for God.

Therefore, you need to get rid of all the pornography that you have. It is toxic waste that is polluting your mind and eroding your morals. Second, make it hard to get more of it. No lock is perfect if you are determined to break it, but assuming you are serious about being godly, put in place hindrances that will give you a chance to question yourself before falling into old, bad habits. I want you to install a free program on your computer that keeps you away from the trash. It's called "K9 Web Protection."