To dream that you are in a cult suggests that you are in some destructive and/or manipulative relationship. You are being exploited. On a more positive note, you have the desire to strive for a better Self. It implies devotion and sense of community.
To see a cult in your dream indicates that you are lacking any spiritual freedom.
To dream that you are a leader of a cult signifies your authoritarian attitude. No one should question your motives or choices.