The Nazi’s gave Bandera an opportunity to kill Russian Communists (Look up Holodomor if you don’t know what that means!). The West was in no position to help him, so he cut a deal with the devil - Hitler to fight in his mind a greater devil - Stalin. If the price was to commit atrocities along the way, then so be it.
So, you think we should have sided with Nazis, too in WW II?
We did align ourselves with the Soviets because the Nazis were the greater evil.