No one can say really what it is only the friends physician or therapy proffessional (therapist, psychiatrist, psychologist) can diagnose your friend.

Trying to diagnose your friend yourself can be quite dangerous you may read more into some things and miss other symptoms completely. Also your forming your own diagnosis of your friend could start reflecting on the friendship by the way you start treating the person when you are in contact with that person. Not saying on purpose or consciously but it can happen. You could also lose this friendship by coming up with the wrong conclusions and so on.

Instead of trying to diagnoses this friend just be the persons friend. You didn't form your friendship of this person based on his mental problems. Leave the diagnosing up to your friend's professionals and just be a firend. That is the best thing you can do for him.