"I must invade a neighboring country to prevent having NATO on my doorstep" - Vladimir Vladimirovich, master strategist "Whoa, if countries are annexed willy nilly then we better join NATO before it happens to us" - Every single one of those doorsteps
It was never about NATO. It's about the Bessarabian Gap and the Black Sea. Putin wants the potential invasion routes into Russia.
The invasion occurred because of Ukraine's movement toward the EU which, eventually, would curtail the ability of Putin and the oligarchs to swindle Russias oil and gas wealth through rampant price fixing and kick-backs. Everything else was rhetoric.