What was it that convinced Reichsführer-SS Heinrich Himmler to start making treasonous deals behind the Führer's back?

Answer 1

At the start of 1945, Hitler appointed Himmler as a military commander on the Eastern Front, fighting against the Soviets. By that point in the war, the German military had been severely weakened, while the Soviet military was massive, powerful, and successful. Himmler, who had very little experience in military command, was an inadequate leader, and failed at the new job. Less than two months later, Hitler fired Himmler. The whole fiasco broke their relationship- until that point, Himmler was considered one of Hitler's most loyal subordinates.

So between the new rift in their relationship, and the fact that Himmler was above the Propaganda and knew what was actually happening in the war, Himmler knew that Germany had no hope of winning the war. In order to prevent the full destruction of Germany, or the conquest of Germany by the Soviets, in April 1945, Himmler began contacting officials in Sweden in an attempt to negotiate for Germany to surrender to the US and UK. His deal was not only rejected, but was revealed on British radio news programs, thus informing Hitler that his most loyal subordinate had betrayed him.