Just after Lucifer realizes he was his own torturer, he has no other choice than to talk Cain into hell, turning himself back into the monster he believed himself to be.
Lucifer: I'll never get to see her again. Chloe: I know. I still can't believe it. Lucifer: Well, at least you'll get to see her, Detective. Eventually. In heaven. But I, well, she's gone somewhere I simply can't follow.