Ukraine is not a NATO member and has never been a NATO member.
Ukraine has the right to choose unions for itself, and Russia, as it has repeatedly agreed, does not have the right to dictate this choice.
Each sovereign country has the right to choose its own security arrangements. This is a fundamental principle of European security, which Russia also supported (see the Helsinki Final Act).
Furthermore, when Russia signed the Russia-NATO Founding Act, it pledged to "respect the sovereignty, independence and territorial integrity of all states and their inalienable right to choose how to ensure their own security."