Well right now, BADLY. Prior to this, he was doing all right again, aside from his general frustration at camp fucking with his friends. He is having some issues with being unable to protect people, stemming from the Eric/Parker incident so the new vampire probably isn't exactly helping. Nor was Chris getting spelled by the spirit or Ebi ended up de-aged against her wishes. Zero functions best when he believes he has a purpose, you know a reason for not offing himself, so his mentality suffers especially when that purpose is threatened. His current feeling of helplessness, augmented by his concern over his own stability, is making him much more agitated and terse, even around those closest to him.

In general, Zero's sanity fluctuates based on both camp's influence and SOMEONE'S presence. People are trying to help him deal with this is various ways, but as we all know, Zero is VERY VERY stubborn and tends to shut them out. Pretty much, he's thrown his whole weight into doing whatever he can during this crisis and he's likely going to crash and burn.

I WILL GIVE YOU QUESTIONS ANYWAY. Tell me about Yuuki and Ruka.