I think in simple terms, Ukraine is an important strategic asset for Russia, and eastern Ukraine is close to Russia culturally (while western Ukraine is not, and increasingly closer to Europe culturally). [Of course, Putin's reputation as a hard man and nationalist, which makes him popular in socially/politically conservative Russia AFAIK, plays a part in the decision making and strategy to reinforce this image, but it is perhaps not the whole story.]
Meanwhile is Ukraine an important strategic asset for the EU or NATO? Not really, as it is not a member of NATO and NATO are
not coming to Ukraine's defence.
[The lack of defence is perhaps for various reasons, first that it is not an important strategic asset for NATO, and secondly that it could/would start a world war which would not be worth it given Ukraine is not a strategic asset for NATO.]
So in that way it was perhaps remiss for the EU and NATO to encourage Ukraine to become a member state, serving to antagonise Russia, and then renege on the arrangement. Consider if Canada, Mexico or Cuba were to have a close security relationship with China and host Chinese military bases etc, would the US be pleased? Or if Ireland were to have a close security relationship with Russia, would the UK, France and Netherlands be pleased?
As for not caring about military or civilian deaths, that is true of course, but applies to any politician ordering a war including Western politicians. Civilian deaths are of course abhorrent.
Anyway, I am wildly out of my depth on Geopolitical matters, I think we should leave that to people with politics and history degrees, unless some of you folks paired history or politics studies with your engineering, maths and science degrees.