It is a misconception that Stalin trusted Hitler. He didn't. He was aware of the danger that Nazi Germany posed to the Soviet Union. However the USSR wasn't ready for war yet, and Stalin was, um, stalling (I'm so sorry^not ^really ). His efforts to reorganize the Red Army and militarize the Soviet economy indicate that he was preparing the country for war and taking the threat seriously. However he didn't anticipate that the war would begin so soon.

Why did he ignore the mountain of evidence that Hitler was about to invade? Well, while there was a lot of evidence, much of it was too vague or contradictory. It is now, with the benefit of hindsight we can say that it was clear what was about to happen. Back then things were much less black and white. It is difficult to know what evidence you can trust and what is just noise. The Soviet Union didn't have very good intelligence analytics at the time.

Secondly, it was illogical for Hitler to invade the USSR at that time. He was still at war with Great Britain. It would make sense that he might want to end that war in some way before invading the USSR. Also there was no obvious casus belli. Usually wars don't start in a vacuum.

Lastly, even if Stalin had all the evidence that a German invasion was imminent, there was not much he could do about it. Declaring mobilization would have been highly provocative and would trigger an immediate German reaction. (Recall that the Russian mobilization on the eve before WWI was essentially made the start of that war inevitable.) Stalin didn't want to jump the gun.