Good that we established who was, is, and will be the aggressor. I'm looking forward to the mental gymnastics about those who invade being actually the ones who defend themselves. As is the tradition in the Russian propaganda, invasion of Finland, Baltics, Poland etc. were all just defensive wars.
But I'm more optimistic about that and don't believe your empty threats. If the NATO strengthens its eastern border, Russia's military has simply no chance there. It's a suicide, it doesn't make sense to bang your head against the wall. Russia has many other weaker neighbors it can abuse instead.
> Ukraine was in the process of ditching its buffer state status by choosing a side.
Ukraine was invaded because it wanted to get closer to EU in the form of the association agreement.
Interestingly, the roughly analogous CIS was never a problem in this concept of "buffer state". Or does "buffer state" actually mean "Russia-aligned"?
And that's the crux of the issue. You can stay as a buffer state only as long as you're a Russian puppet.