different chars, different story. emotional attachment towards Hawke's/Warden's companion is irrelevant... theoretically, in perfect world.
in practice my knowledge of said character will be greater than inquisitor's - i know Morrigan is manipulative and left Warden on the eve of the battle, the inquisitor doesn't (or doesn't care). i'll do my best to RP but i think my PC will have a serious problem with that girl. same thing with Cole - i just know too much about this guy from Asunder. unless they'd undergone some serious changes (ohai Anders), i don't think i'll be able to RP properly.
with chars i like, there is no such problem - i can RP anything, even killing them and laughing maniacally over their dead body.
it's like strawberries (or pick whatever you hate). you cannot pretend to like them and eat whole bowl of them. this would only end in disgusting fractal on the floor. but if you like them, you can pretend you hate them and eat later (playing DA:O or DA2)