Anyone who willingly takes Haer Dalis and invests himself in BG2 romance deserves getting cucked.
Haer'Dalis is CN, meaning working best for a Chaotic or Neutral Charname/party composition, meaning if you strictly roleplay the axis, you should be in a romance with Jaheira. Also, the dialogue(s) Jaheira has with Haer'Dalis are much more telling about his... touch-and-go approach to relationships.
Also... Haer'Dalis is *never* a bad choice. Not only he has access to thief-only high level traps, he also can equip any item, and can easily switch between tornado of death, and tank.
You really want a bad choice, look no further than Nalia. That's a bad choice. lol