I do not mean this to sound trite, but if I have the option of believing your neighbor or an internationally monitored referendum in which nearly 85% of the population participated and over 92% voted for independence from Russia, I'll pay a lot more attention to the referendum. Secondly, the provinces of Kherson and Zaporizhzhia are in southern Ukraine. Kharkiv Province is in eastern Ukraine, staunchly independent of Russia, and fought a successful guerilla campaign for the first year of the war until the Russians were driven out by the Ukrainian army. The capital, Kyiv, is in Eastern Ukraine and is staunchly Western in outlook.
The largest pro-Russian minorities are in Crimea, Donetsk, and Luhansk. Much like the exploitation of the Vietcong in South Vietnam, whose sympathizers made up at most 30% of the population, the Russians were able to exploit the pro-Russian minority in Donetsk to destabilize the province setting the conditions for invasion.
Xi and Putin reached an agreement with respect to this invasion because Xi saw the opportunity to recreate a belligerent Russian military state that would threaten Western Europe and US interests thus diverting our ability to focus on the Western Pacific. If Russia emerges from this with a victory, it will have regained the momentum it needs to embark on just such a roll, as it replaces its battered forces with a truly modernized army. Hence, what happens in Ukraine is a critical US national interest.
That the US can not afford to support Ukraine is the single most nonsensical argument to make about our involvement. Since the beginning of the war, 3 1/2 years ago, we have provided about 165 billion in support, and much of that was simply an accounting drill as we handed over mothballed military equipment and aging munitions stocks. During the same period the US government spent Nineteen point Three Trillion Dollars! What we have provided in support, truly isn't even roundoff money. As a cost of securing a critical national interest, it is a miniscule investment compared to far more expensive and questionable outlays made over the last fifty years.