#edited to add the extra one for wyll i didn't know about until i dug through the game files more!

[vorestarr]

what Sceleritas Fel says about each of the companions if the urge compels you to kill them:

Astarion: "He is so afraid. So, so afraid. Of everyone, besides you, who he ought to fear most."

Gale: "He thinks he might end the world. But you and I could do far worse."

Karlach: "She thinks she is finally away from the monsters. Poor fool."

Lae'zel: "She came all the way to this world, just to die here."

Shadowheart: "The gods fight over her, but is she truly that special?"

Wyll: "He has his own devil, just as you have me. Aren't you a foul pair?"

Wyll (if he's been turned into a devil): "He is an insult to the name of devils, posing as a monster with that sickly good heart."

and then, later, when you're arguing not to kill them:

Astarion: "You like him for more than his looks, but he will never believe that. Why not make him a pretty corpse?"

Gale: "He would forget his god for you. But you won't for him, of that I know."

Karlach: "She's as good as dead anyway. She won't be saved by the power of love. Not yours."

Lae'zel: "She is only using you. Don't you know that?"

Shadowheart: "She was starting to trust you. The only one she ever has. Pity it's coming to an end."

Wyll: "He adores you so blindly. Like a pup. Don't you find it sickening?"