Ukraine was simply the excuse, Putin doesn't want NATO next to his country, which was also a country that belonged in the Soviet Union, a large part of their territory is Russian and their citizens are Russian - speaking for the very same reason.
The war isn't going to stop anytime soon, unless Zelensky surrenders and meet Russia's demands, something which is currently highly unlikely. Putin will keep going till he gets what he wants, one way or another.
Well, Russia already have NATO next to their country - It's Poland and Baltic states. So, Ukraine wouldn't be different, but Ukraine becoming NATO members probably would hit Putin ambitions very hard because he don't consider Ukraine as independent country with their history.
And fact that big part of Ukraine people think and speak Russian doesn't makes them into Russians, you can ask some forum members about it. For example Kharkiv or Melitopol is cities where majority of people speak Russian, but nobody welcomed Russian troops with flowers there. Nobody don't want to have Russkiy Mir there.
Ukraine shares many similarities with Russia, as an ex-Soviet country, there are many Russian-speakers. I've read that the Ukrainian government was putting immense pressure on Russian-speakers, while they were being treated differently, not sure how accurate that is. From what I'm aware of, Putin was expecting to be praised as a savior in Donetsk and Luhansk, but instead, he met resistance.
That's pretty sensible, who in the right mind would praise someone for bombing his city, killing civilians and destroying their properties in the process, even if Putin's claims about the living conditions there were correct.