He should have been with the horses all along (after his brother's intervention before he even left London) but the message was delayed, and when the General received it he refused to move Chrissy because he was the only officer with much intelligence. I think he was also pissed off at being told what to do with one of his own officers.
Then yes, Christopher mortally offended horse-guy, who would have been his superior had he moved there. But yes, he had to be moved because he punched Potty and then accused the other General (who already had it in for him) of being drunk.
I think Sylvia is incredibly angry with Christopher because she can't manipulate him in the way she can virtually every other man on the planet. She wants to break him like a wilful horse, even if that means she denies herself human touch for five years! She's very stubborn.
I have to say Diddl, that I think his behaviour on the train with Sylvia was supposed to have been completely out of character, and he felt very guilty about it afterwards.