Obviously, it was more "uneasy" for some than for others.
Some reveled in it and the US government was shot through with "Uncle Joe" Stalin's spies, who kept him fully informed as to what we were doing, most notably on the Manhattan project.
Turns out, "Uncle Joe" knew more about Manhattan than VP Harry Truman did!
Not FDR's fault, you say?
Well, then consider this -- FDR's administration had no problems seeking out, hunting down and rooting out Nazi spies & supporters.
Even suspicion of collaboration was enough for FDR to put pro-Nazis in camps.
But FDR never found even one Soviet spy, never even looked for them, didn't seem to care.
And US aid to "Uncle Joe" was massive, much as the Soviets denied it ever since, it was critical in keeping the Soviet war-machine running.
So it wasn't just that we were on the same side, we were right there massively helping and also letting Soviets steal our best secrets.
And the result was, we achieved Unconditional Surrender of all the Axis powers, who are today some our our closest friends and allies, while "Uncle Joe" has been restored to honor throughout the Russian Federation and has been reincarnated in the form of Old Soviet KGB Col. Vlad the Invader.
Of course, I'm not comparing George Soros to Uncle Joe, but necessity can sometimes make for strange bed-fellows.