No one is going to invade nuclear armed Russia. Poland and other countries have the right to join any military alliances they want to, they are free countries, not forever lackeys of Russia.
Yeah they are free to make their own decisions and they did - an incredibly foolish one. They would have to be delusional thinking Russia wouldn’t respond in the way they did. There’s video out there showing Ukrainian soldiers saying Kiev better hope the Russians get there before they do, because they want to take care of Zelensky themselves. The Ukrainians have been played for SUCKERS, and now they will suffer the consequences of their own stupidity.