NATO/US are leading the war effort (commanding officers), and Zelensky is said to be refusing their ‘advice’ at some points. He has a job to do and he’s not letting military strategy get in his way.
Ukraine can’t negotiate with Putin for the simple reason that he will take the opportunity to breathe before attacking Ukraine again.
In 2014 when Ukraine gave up Crimea, and de fact the Dontesk People’s Republic and Luhansk people’s republic, there was some hope on the Ukrainian side that Putin would be satisfied with his pound of flesh.
But he was not - he came back for the head, attacking Kyiv.
Putin can’t be trusted for that reason.
When he goes then Ukraine may decide to negotiate with Russia