Nope, the USSR/Stalin didn't become hostile/uncooperative towards the west until after WW2. If they had wanted to conquer "all of Europe except for the UK, Ireland and Spain" they could have done so. They actually wasted time/dallied their run on Berlin to give the allies time to land in France and fight to Berlin so they could take it together. If they had wanted too they could have zerg rushed the Reich and the UK/USA/Canada would have been lucky to meet them at Paris.
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1: The USSR never allied with Germany, it asked to (after Britain/France refused to ally with it) but Hitler refused so Stalin got him to signed a nonaggression pact instead.
2: That pact turned out to be worth about as much as any of Hitlers "I won't invade you" promises, because he invaded the USSR during the war.