Why was he not willing to share his bad mood with me?

maybe you're just thinking too much. just wait for a while- give him time to sort things out. sometimes the more we ask, the more they get away. just be patient.

maybe you just need to give him a little bit space to compose himself,to cool down his bad mood

I guess he just needed some space, some people find the best way to deal with their problems is to sort them out on their own without talking about it with anyone else, they find that they can manage that way.

It's evident that he is puzzled by something,you should try to attention to his feelings and find out fact.

Maybe, he would like carry it alone so that you won't be problematic as he is right now. Maybe he just wants you to live a happy life rather than him making you sad and problematic.

maybe he must have thought not to disturb or upset you by sharing his problem??

Sometimes we are all in a bad mood but since there is really nothing anyone can do to help, we really do not want to talk about it. When my guy is in a bad mood, I just ask if there is anything I can do and if he says 'No', I figure it is NOT me he is unhappy with and give him some space to work through it. If it is important he will tell me about it later when he is calmer. Try not to take it all so personally, trust me, if it is you, he will let you know. However, that said, if the bad moods are happening all the time....I would react differently. Good Luck to you....