There's a romantic ideal of a resistance movement that needs no outside support. But the reality is the US needed support from France to gain independence from Britain, Vietnam needed support from Russia and China to get independence from France and the US, Afghanistan needed support from the US and Saudi Arabia to get independence from the Soviet Union. And on and on the list goes. So yes Ukraine needs support from other countries to maintain their independence from an invader.

In geopolitics the rules are fairly consistent but the players may take on different roles in different scenarios. Sometimes the US is invading a country (bad) sometimes the US is supporting a country defending themselves from an invasion (good). Of course even that's an oversimplification, but try to break free of the nationalist idea that certain countries are always the good guys while other countries are always the bad guys. Think more on what a country is doing rather than feelings about whether a country is good or bad and you'll have a better understanding of geopolitics.

The Soviet Union died long before the people fighting in this conflict were even born. It's an odd form of colonialism to for someone from the outside to think that imposing a solution to a conflict that involves two countries going back to a life that neither country wants all because it fits with their ideal on what these countries should be.