As a retired Probation and parole Officer I am of course familiar with compulsive liars, perhaps in he more extreme form than we find in our society.
My experience in dealing with this personality disorder has taught me over and over again that the compulsion derives from a low self-esteem, that is not fully acknowledged. I see the self-image as being at the root of our personality, and basically liars and con-men are people who are not happy with the way they see themselves.
Sometimes this is associated with a metabolic disorder that can be treated nutritionally, but most of the time these people get better if they can improve their self-image.
We have at our web site a self-help
PSYCHOTHERAPY course that helps people to improve their self-image. Having a negative self-image usually creates defence mechanisms that will upset other people, who then react to us in a negative way. Hence we have a SELF-FULFILLING prophecy.
The course, which is free of charge, consists of eight chapters.It starts off with a consideration of Transactional Analysis, a big word for simple ideas. It explains how we communicate with other people and especially how we communicate with ourselves.
Doing this course at the rate of one chapter a week should help you to feel much different about yourself. It would be a good idea to do this course with your friend, because, believe me, both of you will learn how the minds work.