There is a literally 2 hours long historical lecture from Putin, explaining in great detail why (to his opinion) Ukraine doesn't and shouldn't exist as a sovereign state and "in fact" never was, since the beginning of the history, LMAO. This is what really concerns him, if you listen. In his reality, Ukraine is a Russian province, not an independent state.
He goes as far as justifying Hitler's attack on Poland ("they made him to attack by not voluntarily giving away their territory, it was Poland's fault") — sic. You see where he goes?
So it seems that NATO didn't bother him very much, it is just a red herring or "diplomatic speak" to express his true concerns. The real issue is Ukraine's sovereignty / independence. Joining NATO is just an act of that sovereignty, that couldn't be tolerated.