Metal Gear Solid V: The Phantom Pain - Every Screenshot You Need To See
16. Ocelot Is Snake's New Partner In Crime
Ocelot was shown to have compassion towards Big Boss in MGS 3, both when the latter showed him the 'beauty' of a revolver and also near the end when he helps you out against Colonel Volgin.
It seems like those furtive few interactions have helped bring the two of them together following the revelations at the close of Snake Eater.