Except the Ukrainians are not making any gains. They have only managed to penetrate the zone of control, the so-called "Gray Zone" that extends 10-20km in front of the actual Russian defensive lines.
Tell me how many people have the Ukrainians liberated?
I will tell you: ZERO. They have only taken abandoned villages and small settlements. The name of one of the places they "reconquered" translates literally as "Five Houses".
Ukraine was never a country until Lenin made it one. Even then, it was controversial and led to a huge civil war on the territory.
Lemberg (now Lviv) should have stayed part of Austria, but NOOOOO. They wanted to be their own nation. I say fine - set up a country called "Galicia" in the west and be happy with that.
Just don't go trying to grab the Russian territory in the east and south.