Wow ...this hits right on with what is called an "entity attachment".
Tell your friend to check out this book, i believe it will help him tremendously.
Amazon.com: Remarkable Healings: A Psychiatrist Discovers Unsuspected Roots of Mental and Physical Illness: Books: Shakuntala, M.D. Modi
I posted about entity attachments in an earlier thread on here:
Entity Attachments
Your friend should check that out, too.