"...I have to, though. I will..." Elizabeth's response is quiet and haunted, because she's thinking back to her conversation with Robert. That revelation that killing Comstock unravels everything, and she wouldn't remember anything. The choice would be made, by her, somewhere and someday.

And she wouldn't know any of them. Robert, Booker, or Gai. She would sacrifice her life up until now for a different, unknown one.

Without warning, Elizabeth pushes herself up to where she can reach Gai's lips and kisses him with a ferocity she hopes will pull those thoughts out of her for a moment. She doesn't want a new life. She knows she wants this one.