why didnt the UK make a peace treaty?????

Because Hitler's vision of a Europe under the domination of a single continental hegemon, quite apart from the evils of Nazism, was antithetical to British foreign policy for over two hundred years. It's why Britain fought the Kingdom of France for a century, backed coalition after coalition against Napoleon for twenty years, then allied with France against Imperial and Nazi Germany when it replaced France as the most likely threat to the European balance of power. A single hegemon in control of all of Continental Europe's resources and the Channel Ports is an existential threat to Britain's security and trade. This is why it never accepted Wilhelm's or Hitler's offers of alliance, which were conducted in the assumption that Germany could have Europe while Britain could have the oceans.

Additionally, Nazism had proven itself to be impossible to deal with: Hitler had broken treaty after treaty and had followed every act of appeasement by demanding more. By 1940 Hitler's Germany was no longer a power that could be trusted to keep compacts. Furthermore, and contrary to popular belief, outside of a handful of vocal exceptions, the British elite was at best ambivalent towards Nazism, while the British people were on the whole disgusted by it, especially after such incidents as the annexation of Czechoslovakia in 1939 in violation of the Munich Agreement, and the Kristallnacht pogrom against German Jews the previous year: the British Foreign Office, then still attempting to appease Hitler, openly admitted that Nazi Germany's violent antisemitism was a major stumbling block in finding an accommodation with Germany that would have been accepted by the British people.

Finally there was the personality of Winston Churchill himself: his grasp of history meant that he understood early that attempts to appease Hitler were doomed, while he was especially revolted by Nazi antisemitism. No less a figure than Clement Attlee recalled that Churchill burst into tears when recounting to him the crimes the Nazis were committing against Jews as part of the state-mandated boycott of Jewish businesses after the Nazis came to power in 1933. The appeasers were discredited by the invasions of Czechoslovakia and Poland. The May 1940 War Cabinet Crisis was perhaps the closest Britain got to offering terms, when the Foreign Secretary Lord Halifax advocated for negotiating with Germany through Mussolini's Italy. However, Churchill's position as Prime Minister was secured when the Labour Party under Attlee made it clear that they, like him, believed that negotiations with the Nazis would be fruitless and that they were resolved to continue the war. The former Prime Minister Neville Chamberlain (and leader of the Conservative Party; Churchill wouldn't become leader until October 1940 when Chamberlain resigned the position, a month before his death from bowel cancer) sided with Churchill, effectively solidifying his support in Parliament. What little peace party there was in Britain was discredited after this incident and ensured that anyone who was likely to succeed Churchill should he, for whatever reason, had become incapacitated, would also support continuing the war.

In fact, even before the pearl harbor attack, the UK had already deciphered the japanese codes, and yet they did not warn the USA because UK was looking for allies to stop Germany.

This is false: while Bletchley Park had intercepted Japanese transmissions that suggested that a major offensive in the Far East was in the offing, the reports were vague and most analysts believed that the Japanese were planning for an invasion of Thailand. This report was shared with the U.S. However, the Japanese attacks on Pearl Harbor, Hong Kong, Malaya, and the Dutch East Indies were conducted under strict radio silence; there were no transmissions about them to intercept.

Also, the attack on Pearl Harbor took place simultaneously with attacks on British and Dutch colonial possessions in Asia: to assume that Churchill deliberately withheld this information from the Americans is to also assume that Churchill, a romantic imperialist who effectively viewed Britain's imperial mission as his personal religion, would be prepared to risk the loss of Malaya, Hong Kong, Singapore, Burma, and India for the sake of drawing the Americans into the war. That doesn't seem particularly likely.

Sources

Tim Bouverie, Appeasing Hitler: Churchill, Chamberlain, and the Road to War

Sinclair McKay, The Secret Life of Bletchley Park

Andrew Roberts, Churchill: Walking With Destiny