Someone has said that this is like asking which wing of an airplane is more important! Both are necessary; you can't say one is more important than the other. And the same is true with our faith; it's only genuine if it results in a changed life. The Bible says, "Faith by itself, if it is not accompanied by action, is dead" (James 2:17).
Don't misunderstand me, however; the Bible makes it clear that we are only saved by our faith in Christ, and not by our good works. Our greatest need is to be forgiven and cleansed of our sins -- and only Christ can do that for us. He was without sin, but on the cross He took upon Himself your sins and mine. All we must do is trust Him alone as our Savior.
But when we come to Christ, God comes to live within us by His Holy Spirit. He does this for one reason: to change us from within. He doesn't want us to keep living the way we always have. Instead, He wants to make us more like Christ -- and He will, as we submit our lives to Him every day. The Bible says, "If anyone is in Christ, he is a new creation; the old has gone, the new has come!" (2 Corinthians 5:17).
Only God knows if your friend has truly given his life to Jesus Christ. But don't let his failures keep you from Christ. Instead, face your own need for forgiveness and new life, and by faith turn to Him today.