It sounds like he is going through an unstable period which many of us do over the holidays. I would wait and see what he's like after the first of the year when things get back to a normal routine. If you are down yourself, there is no need to subject yourself to his rantings. Allowing him to do that to you isn't in your best interests, and is giving him more opportunities to trigger himself by his own behavior. I agree, I'd let the friendship go. Don't take on his issues.