I’m thankful for your concern for your friend, and unless he clearly tells you he’s not interested in discovering answers to his questions, I hope you’ll continue trying to help him. God’s promise is clear: “My word … will not return to me empty, but will accomplish what I desire and achieve the purpose for which I sent it” (Isaiah 55:11).
Let me suggest three things concerning your friend. First, pray for him— regularly and seriously. Even if you answered all his questions, it wouldn’t persuade him to repent of his sins and give his life to Jesus Christ. Only the Holy Spirit can convict him of his sins and convince him of the truth of the Gospel—and that’s why prayer is so important in seeking to win others to Christ.
Then help him find answers to his problems and doubts. He isn’t the first person to ask these questions; for centuries, thoughtful Christians have pondered them and answered them. Your local Christian bookstore or Christian internet site can help you. The Bible says, “Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have” (1 Peter 3:15).
Finally, encourage him to look seriously at Jesus Christ, as He is found in the Gospels of the New Testament. Doubts fade in the light of Christ! And if he refuses, ask God to give you the courage to confront him with his unwillingness to face God’s truth honestly.