Ukraine was Russia's ally. Russian businesses operated in Ukraine. Russian entertainment was made in Ukraine. There was effectively no borders between Russia and Ukraine. Ukraine was one of the most pro-Russian countries among the post-Soviet countries.
That’s not really accurate. Ukraine was not a member of either defence or economic blocs, like CSTO, or Customs Union, headed by Russia. Also some of the Ukrainian governments were effectively against relying on Russia, Yuschenko 2005-2010.
Yet, there were extensive economic ties up to 2014, and some cultural ties up to 2022. Its not black and white.
Syria rolled over because HTS improved the quality of life in Idlib. Ukraine resisted because russia turned donbas into a corrupt mafia state. People overlook the importance of the little things. Most people are fence sitters but are very aware of the facts on the ground.
Look what being an ally with Russia brought.