Both the textbook and your teacher are wrong. Both the USSR and the Third Reich saw themselves as diametrically opposed to each other on the global stage. One of the neater visualizations of this rivalry was the 1937 Paris Exhibition, where the German and Soviet pavilions tried to one-up each other in size and pomposity- as seen in this photo. This exhibition was not a fluke. In propaganda and rhetoric, each dictatorial regime posed the other as their antithesis.

For the Third Reich, the Soviets were the foremost example of a Judeo-Bolshevik attempt to undermine German culture and racial solidarity. Mein Kampf was clear on this, as was various state propaganda. For their part, Stalin's propaganda organs lumped Hitler in with other fascist movements as the last gasp of monopoly capital that now had to back strongmen like Hitler and Mussolini to prevent a proletarian revolution.

This mutual antipathy went beyond public invective and into actual policies. The advent of the Hitler government led to the closure of secret German-Soviet military training centers by the end of 1933. This joint training was fraught at the best of times during Weimar as neither side fully trusted the other, but a National Socialist government was too unpalatable for the centers' Soviet hosts. Although the USSR did welcome in KPD and other German refugees, any connection to Germany became ideologically suspect for the NKVD and such connections could become a pretext for removal during the Purges. For its part, the Third Reich became host to a number of White emigres and other anti-communists. Hitler's seizure of power also led to major rearrangements on the European diplomatic front. The Soviets began to send out feelers to various Western and Eastern European states for a common bloc to stand against the rogue adventurism of fascism. In the meantime, Hitler began to try and forge a bloc of his own centered on anti-communism. Both of these diplomatic initiatives failed. Many countries in the West and Eastern Europe rightly suspected Stalin's motives and the costs of a Soviet alliance. While the Soviet initiatives bore some fruit in ending the diplomatic isolation of the USSR, it was never fully able to transition to a functional alliance or partnership system. But the meager results of Soviet diplomacy paled before the abject failures of Hitler's overtures for alliances. In short, Hitler did not so much demand alliance partners as he did vassals. Early initiatives to Poland fell flat as did other tepid overtures to would-be partners. The Anti-Comintern Pact of 1936 between Italy and Japan had no real mechanisms for collective action and all three signatories pursued their own foreign policy agendas irrespective of the needs of their partners in the struggle against Communism. Germany, for example, continued to be one of the main supplier of military hardware to Republican China even after the outbreak of the Sino-Japanese War because such trades provided the Reich much needed hard currency and raw materials Japan could not provide. Hitler's foreign policy successes were ones achieved because of other countries' inaction. Even the Munich Pact did not lead to a lasting alliance or partnership with the parties involved, but further diplomatically isolated Hitler on the continent.

The only period at which the two countries seemed to be working together was the brief period of the Molotov-Ribbentrop Pact. This relationship was far from a functioning alliance and more a byproduct of immediate needs and diplomatic mistakes. Stalin's motives are somewhat unclear for making the move to Germany. One interpretation is that Stalin wanted to gain as much assistance from Germany as possible in light of a realistic assessment of Hitler's long-term intentions. The Molotov-Ribbentrop Pact included provisions for German technical assistance and exchange while the USSR provided the German war economy much needed natural resources. Variations of this interpretation would play out in the post-Barbarossa justifications of the Pact with the added twist that since the West had shown it foolishly trusted Hitler more than the Soviets, Stalin needed to play for time. Another interpretation of Stalin's actions was that he viewed the outbreak of war in Marxist-Leninist terms. War between the Western allies and Germany was the harbinger of a final internal struggle of imperialist capitalism. The Soviet's backing of the weaker power ensured that this struggle would be protracted and pave the way for a Soviet-style revolution throughout Europe. This was the prediction Stalin gave to the Comintern chief Georgi Dimitrov, who recorded in his diary:

A war between two groups of capitalist countries (poor and rich as regards colonies, raw materials and so forth)- for the redistribution of the world, for the domination of the world! We see nothing wrong with their having a good fight and weakening each other. It would be as fine at the hands of Germany the richest capitalist countries (especially England) were shaken. Hitler, without understanding it or desiring it, is shaking and undermining the capitalist system.

Dimitrov would explain in various communiques to Communist Parties that while the 1930s Popular Front strategy of allying with Western democratic parties to combat fascism was correct, within the context of war, the ideologically correct view was to see both sides as imperialist aggressors. Communist activism was to highlight the bourgeois profiteering of the Western powers, both of whom controlled large global empires. Within this context, painting Germany as a relatively innocent victim underscored the true nature of the division of the global economy.

Whatever Stalin's motivations, Hitler's was much easier to parse out for the Pact. The Pact not only secured the Polish prize, it also led to Soviet guarantees of natural resources that war would disrupt. In theory, the Pact would also discourage Western intervention on Poland's behalf as it showed them that there was no prospect of Soviet intervention on behalf of Poland. In this respect, the Pact failed, but the resources and secure flank allowed Germany to negate the impact of the British blockade and complete some of its rearmament in time for the campaigns of 1940 and 1941.

The idea that "Hitler thought the USSR would help him in his fight against democracy" is representative of an outdated thesis that still enjoys some currency called the totalitarian paradigm. This thesis gained a great deal of currency during the Cold War and it held that both Fascism and Communism were two heads of the same oppressive coin. As such, both political ideologies saw themselves as the direct political opponents of liberal democracy, championed by the West and especially the US. Totalitarian interpretations really did not take into account the real differences between the two ideologies and, for this question, confused who the archenemy was for Nazi and Communist ideologues. While neither the Third Reich nor the Stalinist USSR's state ideologies had a high opinion of liberalism, they both perceived it as a weak and retreating ideology. The liberal democratic powers were thus not enemies in these opposed Weltanschauungs, but rather a potential weak partner. At the core of a lot of Soviet and German diplomatic initiatives of the 1930s was the idea that they were on the right side of history and that the liberal democracies were either afraid of this reality or could be reluctantly brought to heel.