This is the one with Feynriel's great temptations in the Beyond/Fade. I took Isabela, Varric and Merrill with me. In hindsight, Merrill was a bad choice. She disapproved of me refusing Torpor's offer outright -- +5 rivalry d'oh! She betrayed me when a demon offered her a way to become the savior of her people. No big deal, though. I knew that was coming. And then later when she tried to apologize for it, sarcastic Hawke did what sarcastic hawke does best: she was sarcastic -- +5 rivalry again. d'oh!
Oh well, I did pick up +4 attribute points for solving those two barrel puzzles, and swatting a flying book out of the air.
Isabela was my second betrayal. As I said, no big deal, I knew it was coming, and the demon did offer her a new ship and crew of handsome cabin boys to go with it. Sarcastic Hawke struck again and simply offered to turn around so Isabela could stab her in the back. Isabela replied with, "I like big boats, I cannot lie." 
Later when she tried to apologize for that godawful easter egg line, Hawke forgave her straight away, which puzzled Isabela to no end and she questioned why there was no angry rant about it. Since Hawke and the lovely pirate queen are already in a relationship by now, I got the flirty response of, "I could arrange a spanking later, instead." to which Isabela stood up from her chair, smiled crookedly at Hawke, and walked saucily away, saying, "Oh stop. You'll make me want to betray you more often."
Just thought I'd share, heh. I hope the next ME game has flirty, relationship-y dialogues like that.