You're reversing cause and effect. The new government in The Ukraine after the coup was already going to join NATO. They overthrew the previous government in order to do exactly that. This put Russia in a damned-if-you=do, damned-if-you-don't situation. If they
didn't threaten The Ukraine, The Ukraine would just join NATO and put NATO missiles, etc in its territory pointed at Russia. if they
did threaten The Ukraine, they're "driving it closer to NATO." They went with the latter, because at least there was a
possibility of the Ukrainian government backing down. That didn't happen, so now we have bullets flying.
As for getting a border with 4 more NATO countries, you're buying into the idea that Russia intends to add the whole Ukraine to its territory. This seems to be western propaganda, since
Putin sent out a video speech that he'll negotiate surrender terms if The Ukraine agrees not to join NATO and to demilitarize. If The Ukraine complies, it will still exist as a buffer state between Russia and those other NATO states, although he possibly also intends to take the Donetsk and Luhansk regions, if it looks like he can get away with it.
I don't blame Poland for feeling that way, considering that the west hung them out to dry the last time they were invaded. But as I said above, Russia keeping all of The Ukraine doesn't appear to be the agenda, and this just gives them another good reason not to. If they're smart, they'll steer clear of the Polish border to avoid adding another enemy to the conflict. Of course, military blundering or too much belligerence bringing Poland into the conflict is always a possibility.