You aren't alone in this habit; the ease with which people can gain access to pornography over the Internet today has become one of our most serious moral and spiritual problems. And you're right: Satan rejoices when people get trapped by it, because it appeals to everything in us that is sinful and selfish.
But you aren't alone for another reason: God is with you, and He wants to help you break free of this habit. He loves you, and He hates what this does to your heart and mind. He also knows that it can destroy your relationships with people you love, and lead to a totally distorted understanding of what's important in life and how we ought to live.
This is why the most important step you can take is to turn to God for the help you need -- confessing your sin and your helplessness to Him, and asking Jesus Christ to come into your life. When you do, God will forgive you and make you one of His dearly-loved children forever -- and once you understand this, you'll never be the same.
But God also wants to help you in practical ways. Install software that blocks such sites; move your computer where others can see it; reach out to someone you trust who knows your problem and will hold you accountable. God's promise is for you: "When you are tempted, he will also provide a way out" (1 Corinthians 10:13).