Historically, the Muscowites, Belarussians and Ruthenians/Ukrainians were one people -- the East Slavs arising from Kievan Rus. This was split in the 13th century with the Mongol invasion. After this, Belarus and Ukraine were under the Lithuanian Duchy and then under the Polish-Lithuanian commonwealth. Muscowy was a tax collector for the Grand Khan and then arguably took over the Mongol Empire -- it's traditions politically are more Mongolic, authoritarian.
the Ruthenians were under the more chaotic, more democratic P-L commonwealth and developed different traditions.
But they didn't have time to develop their culture after the middle ages because of the strong Polish national culture. So many Ruthenians became Polonized.
in the 17th century the Ukrainians jumped into the Russian fire and destroyed any chance of them emerging as a separate nation state -- Ukraine was the badlands between PLC, Russia and the Ottoman Empire, so they were more chaotic than the Belarussians
But no time to develop a higher culture.
under Tsarist Russia they were still frontier lands but in the mid 1800s Europe went through a period of nationalisation (thanks to the influence of the French revolution), creating mono-cultures instead of multicultures that had existed prior -- so England stamped out the Cornish language and attempted to do the same with other languages. The French utterly stamped out their local languages (and still do), there was standard German
And the Russians attempted the same. They were moderately successful with other nationalists (Finnic like Mordvins etc) and VERY successful with fell East Slavs
So, I would argue that Ukraine has not had the time to develop a separate identity and is very closely tied to their cousins in russia ethnically and culturally
Putin is using this as an excuse to bite into Ukraine
Eastern Ukraine,populated with Russians by Stalin tends to be pro Russia particularly in the Donetsk region. The rest of Ukraine is very nationalistic with the Ukrainian language and culture predominant. Ukraine does not want to come back under Russias control and IMHO will not