Christians: do you have to actually believe in the existence of Jesus to be a Christian?

Jesus is an admirable character and guide to moral behavior in the New Testament. But the New Testament is fiction, and Jesus is a fictional character. There is no afterlife, and there is no salvation. The best I can possibly do, from a Christian standpoint, is to accept the story of Jesus as a guide to life, to live by Christian principles. After years of study and reflection, there is no way I could possibly believe in the actual existence of Jesus or the Christian God---it's contrary to everything I know about reality.