The Soviets were never "with the Nazis." The Soviets spent years trying to get the West to form an allied pact against the Nazis, insteas the West gave the Nazis Czechoslovakia. The non-aggression pact was paid to buy time, as the USSR was a developing country and Germany a more developed one. Nazism and Communism are diametrically opposed and cannot coexist, in the years of the Nazis rise the Nazis murdered the Communists in Germany first, and the Soviets were constantly warning about the Nazi threat.

The surprise attack by the Nazis was swift, brutal, and with genocidal intent. They took land quickly, but were pushed back into a stalemate, and then rapidly the Nazi line collapsed. Lend-Lease equipment arrived after the Red Army had stabilized, it certainly helped but was not critical to the success of the Red Army, they weren't crumbling. Repeating Goebbels "Russian hordes" anti-Slavic racist talking points doesn't help you either, there are no records of "wave tactics" as was reported by the Nazis. Those records came largely from pre-Soviet Russian tactics, not the tactics of the Red Army.

They didn't "fuck over" a bunch of countries either.