So at least you admit that Russia broke a promise.
As a sovereign state, Ukraine was fully within its rights to join any alliance but the problem for Ukraine was that NATO never considered Ukraine for membership in the first place. Whatever was insinuated was nothing more than chatter.
As for Cuba, what we did was a blockade. We could have invaded, killed all Soviet advisors, and took every missile on the island and there was nothing the Soviet Union could have done. Instead, we let the Soviets carted off the missiles and saved some face.