It's no secret that Russia and the European Union have had a complicated relationship for years. And while there are a number of reasons why Russia may not want Ukraine to join the EU, it seems that the main reason is simply that it would mean that Ukraine would become more closely aligned with the West, and less with Russia. This is something that Russia clearly does not want. And while some may argue that Russia is simply trying to maintain its sphere of influence in the region, it's important to remember that Ukraine is a sovereign nation and has a right to choose its own path. 
Russia has long opposed Ukraine's membership in the European Union, and there are a number of reasons why.

First and foremost, Ukraine's membership in the EU would diminish Russia's influence in the region. Ukraine is a key transit country for Russian energy exports, and Moscow does not want to see Kyiv become a part of the EU's integrated energy market. This would make it more difficult for Russia to use energy as a political tool, as it has in the past. 

Second, Ukraine's membership in the EU would also likely lead to the country adopting Western values and norms, which would challenge Russia's own autocratic system of government. Moscow does not want to see a successful, democratic Ukraine serve as a model for other countries in the region. 

Finally, Russia is concerned that Ukraine's membership in the EU would allow the country to eventually join NATO. This would put NATO's military infrastructure closer to Russia's borders and could pose a threat to Russian security. 

There are a number of other reasons why Russia might not want Ukraine to join the EU. For one, it would lose its influence over Ukraine, which it has used in the past to further its own interests. Additionally, a pro-EU Ukraine could pose a challenge to Russian President Vladimir Putin's own power and authority. Finally, it's worth noting that Ukraine is currently in the midst of a major economic crisis, and joining the EU would likely only exacerbate the situation. For all these reasons, it's clear that Russia has no interest in seeing Ukraine join the European Union.

For these reasons, Russia has been working hard to keep Ukraine out of the EU. Moscow has used a variety of methods to achieve this goal, including economic pressure, political meddling, and military threats. It is clear that Russia does not want Ukraine to join the European Union. Moscow's opposition is driven by a desire to maintain its influence in the region and to prevent a challenge to its own autocratic system of government.