Strategic cooperation between the Soviet Union and the West was minimal during the Second World War, beyond some basic details; the Soviets will do what they want to do (Adhering to agreements regarding spheres of influence, of course).
If the Bomb wasn't used on Japan (not available or whatever), I've seen a suggestion it leads more/less directly to a nuclear war with the SU in the '50s.
Why? Stalin doesn't believe the Allies (U.S.) will use it on civilians (despite the city-burning...).
How credible the proposition is, IDK. It does bear examining.