The Russians have hated the Chinese ever since the Mongols defeated
the Chinese in 1206, and then went on to attack and conquer almost all
the Russian principalities, and made them bitter vassals of the Mongol
Empire, in a relationship called the "Mongol Yoke" that went on for
two centuries. The Russians hate the Chinese.
The Chinese claim parts of Russia's Far East, including Vladivostok,
the home of Russia's Pacific Fleet, and demand that it be returned to
them, like Hong Kong. The Chinese are deeply contemptuous of the
Russian barbarians, and are planning to conquer parts of Russia's Far
East.
Russians love West Europeans and Americans. Chinese are deeply
contemptuous of West European and American barbarians.
Russians and Indians are long-time allies. Chinese and Indians hate
each other.
Russia depends on the South China Sea for commerce. China is
illegally annexing the South China Sea.
Basically, the Russians and the Chinese hate each other, and the
hatred goes very deep. Under no circumstances will Russia and China
EVER be allied in a generational crisis war.