Its not an easy thing to do. I came from this life, and I had help from a friend. But my biggest reason for leaving that life and coming to God is because He showed me what was going to happen to me when I died. I have some advice though.
I did have a Christian friend growing up, he was very devout and serious about the Lord at the time we met (he still is, but has struggled like the rest of us as he got older). I was someone who, at the time, hated God and insulted Him. My friend was absolutely open about his faith in Him, and I knew about it. We had no reason to friends /at all/, but for some reason he and I really got along way well, and he pushed me to be his friend, and was very nice to me, and I ended up really liking him too, and opened up and became his friend.
He knew how I felt about God, and he would talk to me sometimes about Him. And if one of us got to angry, and the conversation got heated, he would change the subject and make a joke to calm everything down.
When I opened up to him about how I wanted to live my life, he wasnt "supportive", as in he didnt tell me anything like "you should be free to live how you want, dont be ashamed", but he didnt react in anger with me either. He just affirmed that he understood what I was saying to him, and stood by Gods word, but still treated me as a loving friend.
He was nice to me, he helped me, he listened to me, he stood by me. He never showed support for what I was doing, but when I faced people who made me feel bad about it, he would listen to me, and tell me he thought they were wrong in doing so, even while standing by Gods word. And because I felt that he actually did love me as a brother and care about me, I stayed friends with him, believing that even though his views were "backwards" and he was just naive and didnt understand the "real world", he was an awesome friend that I could trust. And when God let what happened to me happen, I knew I had a brother in Christ I could run to to help me.
Sorry for the long story, my point is to be loving of your brother, even though he has walked into sin. Dont let him believe you hate him, or that you and he are now enemies, because the enemy will be putting this into his head to keep him from God. Be there for him, and let him know you love him, and that he can trust you. And pray for him. When the conversation about God comes up, dont become angry, even if he insults God. Stand by the word of God, but do it with love. Assure Him that God could help him, and that God doesnt hate him, and that God does hate all forms of sexual immorality, such as adultry, pornography and all these things common in our world. And pray that the Lord help him see why its wrong, and hopefully one day he will answer the Lords calling, and come to Him with trust that he doesnt need to act out on these urges to be happy.
Hope that helps.