I'm glad you're questioning what your friend has been telling you -- because it isn't true. God is real (even if your friend doesn't believe in Him), and I have no doubt that He has been watching over you.
But why has He blessed you in this way? I don't know the full answer; God's ways are often hidden from us, and we'll only have the complete answer to our questions when we get to heaven. As the Apostle Paul wrote, "Now I know in part; then I shall know fully" (1 Corinthians 13:12).
But I'm convinced that one reason is because God wants you to come to know Him and give your life to Him. Yes, you believe that God may have been watching over you -- and you're right. But God wants you to know -- beyond a shadow of a doubt -- that He loves you and wants you to be part of His family forever. In other words, His goodness should make you want to turn to Him in faith and commitment. The Bible says that "God's kindness leads you toward repentance" (Romans 2:4).
How can you know God? Only one thing separates us from God, and that is our sin. But Jesus Christ came into the world to take away our sins, and when we open our hearts to Him and commit our lives to Him, God forgives our sins and makes us His children. Turn to Christ and ask Him to come into your life today.