The Association for Spiritual Integrity
The Cult Education Institute has gathered an enormous amount of information and resources regarding cults and cult-like organizations and movements.
Directing people to end their relationships and telling them there will be dire consequences if they leave the group, are both clear signs of cult like dynamics:
Dare to Doubt provides a great depth of resources for those attempting to detach from harmful belief systems:
Dr. Janja Lalich writes on Cults, Extremism and Undue Influence:
An article from Psychology Today about “The Dangers of Becoming a Spiritual Teacher”.
Also from Psychology Today, an article about cult leaders and narcissism:
Here is a long excerpt from a book entitled Prophetic Charisma about the role of charisma and narcissism in the makeup of many leaders:
And here is another fascinating chapter that explores the psychological dynamics at play in the followers:
This article explains so many of the stories we hear regarding many spiritual teachers that seem to start so clearly and profoundly sharing their experiences. Then they veer off into actions that lack integrity and even sometimes common human decency. The descriptions in the article are helpful in spotting the specific dynamics that are being used to manipulate others by malignant narcissists.
One of countless first hand accounts of experiences with cults and cult leaders:

