Is it friendly, hostile, or just plain grey? You may have a new room mate who's there to stay. Try talking to it, ask it what it wants. Maybe it'll tell you why it haunts.
He sounds quite lonely. Maybe he feels safe with you only.
And what thread might that be? Could you give me a name so that I may see?
Thank you, I'll have a look. I don't mind telling you that ghosts make me a little shook