Short answers, pulled from the story.
Cuba and the Soviet Union formed their alliance in the aftermath of Cuba's 1959 revolution, when Washington's economic embargo left Cuba searching for new trading partners. The two nations signed their first trade deal in 1960, exchanging Cuban sugar for Soviet fuel. From that year through 1990, the Soviets provided all of Cuba's oil needs on credit, at subsidized prices that were never repaid.
The Cuban Missile Crisis strained Soviet-Cuban relations even as it represented the peak of their military cooperation. Castro was not consulted during the Kennedy-Khrushchev negotiations and was furious at the unilateral Soviet withdrawal of missiles. The crisis produced a thaw between Washington and Moscow while simultaneously cooling relations between Havana and Moscow.
Cuba joined Comecon in 1972. Classified as an underdeveloped member country, Cuba could obtain Soviet oil in direct exchange for sugar at highly favorable rates. The hard currency Cuba earned by re-exporting Soviet oil funded imports from outside the Soviet bloc and investments in social services.
The Soviet Union established a signals intelligence facility at Lourdes, just south of Havana, in 1962. The station monitored all US military and civilian geosynchronous communications satellites and ranked among the most significant intelligence capabilities the Soviets trained on the United States. It was abandoned in 2002.
Gorbachev's perestroika created an ideological rupture with Cuba from the moment he took power in March 1985. Castro launched his own "rectification of errors" campaign in 1986, designed to prevent Soviet-style reforms from spreading to Cuba. In February 1989, Castro expelled Soviet diplomats and banned Soviet publications from circulating in Cuba.
Cuba's trade with the former Soviet Union fell by more than 90 percent after the Soviet Union ceased to exist in December 1991. The Soviet Union had previously imported 80 percent of Cuban sugar and 40 percent of Cuban citrus. Oil imports to Cuba dropped from 13 million tons in 1989 to roughly 3 million tons in 1993.