DP spent this morning doing jobs around the house - buying the xmas tree, taking stuff to the tip, getting the decorations down from the loft etc while I looked after the baby and had a lie down while she had her nap (tired as still feeding her at night). After lunch he put the tree up and DS(5) was all excited about decorating it. We're all in the dining room, he's getting the baubles out of boxes, and I'm tidying up stuff in the corner of the room, making more space for the tree. I know I'm irritating him but ignore it. I'm carrying some stuff upstairs to pu away when DS follows me and whispers 'when you were turned away daddy gave you an angry look'. I say 'I know, don't worry, he does that, take no notice'. DP overhears what I said and starts demanding poor DS tells him what he said. I try to gloss over it but can't think of a lie quick enough and tell him. He immediately picks up the car keys and leaves. I ring his mobile and text him saying DS wants to decorate the tree and wants him there, but no response. About 3 hours later he comes back and goes straight upstairs. DS runs after him calling 'daddy, daddy'. (I'm holding the sleeping baby downstairs.) He then comes back down upset, saying daddy said 'fuck off' and shut the bedroom door on him. He is 5.
What is WRONG with him? What would you do? (More constructive than LTB pls).