If it is a case of possession, then the demon in question was lying about everything from the beginning, sounds like he took advantage of your friend's narcissism. That's assuming there is a demonic entity to begin with, and I'm not convinced just from the story. If the end result is chronic fatigue, depression and hopelessness, lack of willpower, etc., then it's one of many possibilities, several of which are purely psychological. Automatic writing does not have to come from an external force, it can arise from within.
Have you considered contacting the local clergy? What experience do you have commanding demons? It's not entirely clear what you're looking for here - confirmation, a quick ritual (exorcisms last sometimes many days), some kind of explanation?
Posting the sigil you have is a good place to start.
The world is complicated - that which makes it up is elegantly simplistic, but infinitely versatile.