For China, Russia is the most important relationship it has right now. As long as Russia is with China, then China needs to fear nothingChina shouldn’t completely trust Russia either.
Relationship is tied together by personal relationship between Xi and Putin, and some shared strategic interests towards the US. It hasn’t stood the test of time.
Russia does not want to become a Junior partner relative to China. Does it serve Russian interests to have a much stronger China at its boarder.
However I am also concerned that after Putin steps down, a power vacuum will appear and who knows what will happen then (hint: West agents will be activated...)