What two people has Montag become and what does he see as the final outcome of acquiring this dual personality?

Montag has become a book burner and a book reader.

As the final outcome of this dual personality he sees that he has to do something he cannot just stand back and watch the world literally burn away. He feels he has so much to save and if he doesnt act soon then no one will stop anything. That is why he goes and talks to Faber. Together they devise a plan to destroy the firemen structure by placing books inside their homes, and turning in an alarm on them.