It turns out that all of you have actually been "controlled" by the tadpoles since the game opened, it having eaten the brain of the person your characters used to be and absorbed their memories. However, the tadpoles absorbed their memories so completely and then never were given any other knowledge by an Elder Brain/the illithid that planted them, so they actually believed that they were the individuals whose brains they had eaten.
The past tense narration thing will turn out to be a part of this, as your character's brain tadpole is narrating the entire story from some point in the future, looking back at its life from the moment it first came into existence. There will be a midgame reveal that shows all this, with several of your allies possibly killing themselves or turning full mindflayer evil depending on how you've treated and interacted with them so far.
Then the story will be your character and friends trying to come to terms with their existence; are they a mindflayer, or does the fact that they have all the memories and sense of self of the original person mean that they are in some way that original person?
