Give him his space when he gets that way. If you are not around his "mood" it is less likely to have an affect on you. Walk away, do something that will make you happy.
Positive self talk, over and over.
Keep telling yourself "Its not my fault"
He has his issues, they are HIS issues not yours.

I do this myself and after sometime it starts to stick.

I wish you all the best, and welcome!