i believe there is no sin so great that God does not forgive. if you look at the story of Moses for instance. when he saw the Egyptian man beating his two brethren (hebrews), he was so angered he killed the man. later in his life, God used Moses to be a great leader and he lead 3 million people out of egyptian bondage.

all sin is forgiven if we confess it with a sincere heart and ask forgiveness.

that is my belief.