Unfortunately there is going to have to come a time where someone calls Putin's bluff. Nobody wants war. And certainly nobody wants nuclear war, but unless you are prepared to accept the alternative of Russia (or any other nuclear power) simply doing whatever the feck they want without contestation, then there must come a point where you say "no".
Putin has threatened nuclear war on anyone who intervenes.
Putin has threatened that banning Russia from SWIFT will be seen as a declaration of war.
Putin has multiple times referenced Russia's nuclear armament.
Much like the boy who cried wolf, he has figured out that as long as you cry "nukes", the rest of the world tends to just idly by, for fear of him following through. It doesnt work. You let him go unchallenged and - just like with Hitler - he gets bolder and bolder. A clear red line needs to be drawn, and the west needs to be willing (or at least to give the impression that they are willing) to enforce those lines militarily.