I would like to point out that in the eyes of many commentators the whole question of NATO expanding east is a red herring, or at least not the most important part of the story. Putin believes that Ukraine should be part of Russia. He says so himself, more than once.
https://www.vox.com/policy-and-polit...pt-february-22
Here's a quote from his speech just before the invasion:
“Ukraine is not just a neighboring country for us. It is an inalienable part of our own history, culture and spiritual space,” he said, per the Kremlin’s official translation. “Since time immemorial, the people living in the south-west of what has historically been Russian land have called themselves Russians.”
Ted