I wouldn't be so quick to blame George III for the loss of America. His prime minister, Frederick North ( 2d Earl of Guilford for anyone who cares )
seemed to spend more of his attention and energy to administering the Exchequer (Treasury) and dealing with the House of Commons. Seems his indifference to the Colonial rebellion got in the way of effective management of the crisis at hand. He totally neglected his role in directing the war effort against the American Colonies and at the same time managed to keep George III totally in the dark as to what was really going on.
Personally, I'm grateful to Freddy North for his sloth, otherwise we'd be flying the Union Jack, singing God Save King Chucky the Threeth, and would be in as sad a shape as the rest of the Commonwealth.