You are mistaken if you believe the US would have supported another three or four years of war against an ally. Already the UK was so war weary that it kicked Churchill out of office and voted in a nebbish, Atlee.
Great word to describe Atlee. And you're right, the Brits were sick of war, to the point where they dumped a giant for a nebbish. That's why they gave us so much grief on a lot of military stuff behind the scenes, because they wanted to win the war in 1944 to get it over with and, in Churchill's eyes, to retain some semblence of the British Empire, and we were going to take as long as it took to do it right. To get an idea of the British mindset, I recommend the diaries of Lord Alanbrooke (British chief of staff, their George Marshall) that cover 1939-45 and were published a while back pretty much in their entirety.