Mario, like Guillermo Cabrera Infante (whose Father was a founder of the pro-Soviet Cuban PSP) was a supporter of Castroism in the 60's, until Fidel's support of the Warsaw Pact invasion of Czechoslovakia in '68 and the Padilla affair ( http://www.nybooks.com/articles/10580 , "An Open Letter to Fidel Castro, signed by Sartre, Gabriel Garcia Marquez, etc.).
Infante's essays on Cuba are collected in, "Mea Cuba, " much of note there, corroborated by another former Fidelista, Carlos Franqui in his, "Family Portrait With Fidel." Franqui was a early cadre in M-26 and an editor of a Cuban revolutionary arts journal.