did not read the book, it would be explain to me more, probably, but looking a film I have drawn absolutely other conclusions - not Gregorio was revenges Manuel, but friends Gregorio (they was betrayed Manuel, too) and own conscience. Manuel the kind, good person, but he have one defect - he should betray and he betrays for the sake of love which he searches in different people and finds, but it does not suffice him, he the addict of love - all women for him is marijuana type, only Tania - opium. I think it's a magnificent film though with it is easy pornography, and Diego Luna creates a fine image of the person lost in the feelings
