Short answers, pulled from the story.
In November 1945, Soviet commander Rodion Malinovsky ordered the Red Army to transfer Japanese weapons to Chinese communists. This action followed a secret agreement between Joseph Stalin and Chiang Kai-shek that required the withdrawal of Soviet forces from Manchuria.
Mao Zedong denounced Nikita Khrushchev as revisionist traitors in 1961 because Khrushchev delivered a speech titled On the Cult of Personality and Its Consequences in early 1956. This address denounced Joseph Stalin and initiated de-Stalinization across the Soviet Union which Mao viewed as an attack on their ideological foundations.
In December 1960, Khrushchev withdrew 1400 Soviet technicians from the People's Republic of China which cancelled approximately 200 joint scientific projects. The Soviet Union also ended 600 contracts with the People's Republic and routed grain shipments to feed the Soviet Union instead of starving Chinese citizens.
On the 21st of August 1969, President Richard Nixon secretly informed embassies worldwide about potential Soviet military options and decided to intervene. He warned that America would launch attacks on approximately 130 Soviet cities if they attacked China which caused the Soviet Union to abandon its planned attack shortly afterward.
Mikhail Gorbachev visited China in 1989 shaking Deng Xiaoping's hand to end decades of hostility between the two nations. This meeting occurred right before Tiananmen Square Massacre in June 1989 where Soviets expressed diverging opinions regarding the events.