When some people come to Christ the change in their lives is sudden and dramatic (as it was when the Apostle Paul met Christ). Others, however, change only gradually, and may seem like they are on a spiritual roller coaster at first (such as the Apostle Peter). Jesus compared God's work to a small mustard seed that may take a long time to grow after it is planted (see Mark 4:31-32).
Only God knows your friend's heart, of course, and whether or not he has truly given his life to Christ. However, if a person's life does not change in any way, the Bible warns that their "faith" is false, and they have not truly opened their hearts to Christ. The Bible says, "As the body without the spirit is dead, so faith without deeds is dead" (James 2:26).
Many people today, I'm afraid, say they believe in Christ, and they may sincerely think they do. But their lives show no evidence of it; they live only for themselves, and they show no interest in obeying God or becoming more like Jesus. As a result, they are in a very dangerous spiritual situation.
Pray for your friend, and ask God to help you share your concern with him. Most of all, be certain of your own commitment to Christ. Have you turned your life over to Him, and are you seeking to live for Him every day?