It seems as if it is the same pattern of behavior your son displayed the first time his Dad left, he is probably concerned for his Dads Safety as I am sure he has overheard some scary things,is there anyone around your son uses bad words and does he see perhaps on TV and Video's any violent behavior he could be emulating?very often it is a learned behavior.,Perhaps you have to get tough on him and set firm bounderies, if he acts out he should have repercussions and do without a favorite Game or TV or the PC games,the school shoul;d have bounderies for him aswell, Talk to him and tell him you will not permit it anymore and tell him what you will be taking away as reprisals, give him the choivce, and be consistant and mean what you say. Make sure he has a lot of Physical activities of the positive kind , sports ,Ball games and Cycling, running and Fun.
I really do not have any advice as I have not been in your very difficult situation. I do have some knowledge about anxiety though. Whether your son is suffering from anxiety or stress is irrelevant - I think you are asking if your son suffers from an anxiety disorder and I doubt that very much. But yes, I suspect he is suffering from anxiety/stress from the impending change. It's too early to know if the counseling program is working; if not, perhaps the school or your son's pediatrician could offer a suggestion to better help this child . Perhaps others on this board might be better able to help. I feel for you and wish you the best ...