All the statements of Ukrainian politicians that they were promised that Ukraine will be accepted into the Alliance are PR and nothing more. For NATO countries, Ukraine is important as a buffer zone, but not as a member of the Alliance.
Summary
Crimea returned to Russia in 2014, based on the results of the referendum in which the overwhelming majority of the region’s population expressed their support for this step, against the backdrop of the deep political crisis that led to the overthrow of the Ukrainian government headed by Viktor Yanukovych.
Disproof
Recurring pro-Kremlin disinformation narrative about the annexation of Crimea, claiming that Crimea voted to rejoin Russia through a legal referendum.
The demonstrations which began in Kyiv in November 2013, called "Maidan", or "Euromaidan", were a result of the Ukrainian people's frustration with former President Yanukovych's last-minute U-turn when, after seven years of negotiations, he refused to sign the EU–Ukraine Association Agreement and halted progress towards Ukraine's closer relationship with the EU as a result of Russian pressure.
Crimea is a part of Ukraine and was illegally annexed by Russia. In 2014, Russian troops obliged the parliament of Crimea to organise a referendum, which was illegitimate under international law, and then formally annexed the peninsula and brought it under Russian territorial control. The annexation has been condemned by the UNGA (see the resolution A/RES/68/262 on the territorial integrity of Ukraine).
No international body recognises the so-called referendum, announced on 27 February 2014 and held on 16 March 2014. Following the covert invasion by “little green men,” the referendum in Crimea was conducted hastily and at gunpoint, barring impartial observers from entering the peninsula.
A year after the illegal annexation, Russian President Vladimir Putin admitted that the plan to annex Crimea was ordered weeks before the so-called referendum.
The European Union does not recognise Crimea's annexation and continues to condemn it as a violation of international law. EU sanctions continue to be in place against Russia as a consequence for the annexation. For the EU statement on the sixth anniversary of Crimea annexation see here.
Read similar cases claiming that Crimean people have expressed their desire to rejoin Russia in a democratic process, that Crimea never belonged to Ukraine, that Crimea’s reunification with Russia was legal, or that historically Crimea was a Russian land.