As far as Catherine knows, she's not connected with any injury or any misfortune of the general, except for her flight of fancy that he surely can't be aware of.

My best guess for "who ever am, etc" is that the "etc" stands for something like "your affectionate brother, James", and once we comb out the fancy word order we get "from James, your ever-affectionate brother". But I really don't know, never having seen that form of words anywhere else.