This is a tough one to figure out. It does seem that something about the vacation together impacted him in a negative way. But there seems to be no clue as to what that was. It sounds as though he may be a lot less verbal than you are, and he may have a lot going on in his head that he has not shared. Getting him to share is what is needed, but that can be a major challenge.

He may genuinely be in a quandary about what it is that he wants to do. Again, getting him to talk more seems like what is needed.