That is true but there is a history. While it is a prominent Kremlin talking point, there is a civil conflict in Ukraine. The initial reason was that some wanted free trade agreements with the EU while others did not, because it would mean their industry breaking down due to more competitive European alternatives and investors buying their infrastructure.
But this is not an ethnic or cultural conflict. You have Russians and Ukrainians on both fronts of this conflict.
While most Ukrainians are nationalists, it is very true though that the Maidan factions is vastly more interested in democracy and the Anti-Maidan one, or whatever they call themselves now.
More info:
https://en.wikipedia.org/wiki/War_in_Donbas
Ukraine is complicated. You have to read up a lot. Probably begin with the orange revolution but even the time before and the relation to the EU and US is important.
To take sides here until the internal conflicts are resolved basically means supporting another proxy war. If it isn't already one because the factions are dependent on outside help to keep up the fight. The south-eastern Russia associated group certainly more so than Kiev and co.
The conflict also hits innocents, the MH17 to Malaysia with a lot of Dutch people got shot down by the Russian associated group.