First of all, congratulations on opening your eyes and being willing to listen. That's not a small step. Please start with cfgaussian's post, as it's comprehensive and detailed. But I like to keep these two links handy for my liberal friends who call anything written by non-western people propaganda. They both basically say the same thing, but the first is more historical, and the second is more geopolitical. The second one is written by a former assistant secretary general of the UN who "escaped" the USSR.
https://www.meer.com/en/74782-will-the-ukraine-war-be-the-undoing-for-the-european-union
Personally, I'm entirely on board with the Russian "invasion", and my support for it is uncritical. The war should never have happened, but now that it's here, Russia needs to see it through to the end. They were left with no other choice.