Board Thread:Metal Gear Solid V/@comment-181.59.111.38-20150922004033/@comment-109.193.182.64-20150922072519

He leaves Diamond dogs along with the phantom sometime between TPP and the very first MG game settled in 1995.

SPOILER ALERT:

In the post credit conversation with Ocelot he states that he feels betrayed by BB. It seems he feels abandonned after all they've been through and has a grudge against BB for leaving him to do the dirty work without letting him know anything. As far as I understand, he decides to help the Phantom instead, who after all seems to be the "New BB". It's not his intention to help Cipher.

However considering the events of the very first MG game, it seems, that the Phantom is loyal to BB till the very end. The Phantom trains Solid Snake along with Miller to infiltrate Outer Heaven. During Snake's mission, the Phantom unveils his loyalty to BB and betrays Snake and with him Miller. Along with Solid Snake he worked for chipher without actually realising it. So Miller's fooled time and time again by both BB and Cipher.

In MGS1 the conversation between Miller and Ocelot from TPP makes sense: Miller unknowingly worked for Cipher by being a consultant and an advisor for Snake. Ocelot told Miller, that if he turned to Cipher one day, Ocelot would aid the other son. In MGS1 Ocelot aids Liquid (at least to some extend) and we learn, that he was killed in his house 3 days before the incident. We don't know if it was Ocelot or Liquid, but Liquid must have known at least something about what was going on.

Miller's like a handicapped version of Solid Snake: Always kept in the dark by everyone until the very end.