Board Thread:General Discussion/@comment-79.52.61.188-20130415085048/@comment-42.98.54.216-20130710132255

Okay I am being lazy and read only the very first few posts and remembered what The Boss said to Jack http://www.youtube.com/watch?v=hbLeMfhGoCI

Enemies are only in relative terms and it changes with times. The only thing you can believe with absolute certainty is the mission.

So, it could just be - Big Boss and Zero befriend each other again because of a common enemy or interest. Simply because they parted ways in MPO doesn't mean this will not happen. Perhaps they need to fight the Russians together, who knows?