I'll tell you another that made me cringe for different reasons. Jack.
Watching her lay in bed crying during the sex made me realize than she really needed a friend more than a boyfriend. I almost wonder if Bioware has ever done this on purpose like "Well Jack would go for it but we're going to show the player that she is not in the right state of mind to be in a relationship right now." That could be interesting if it were a little more obvious that it was intentional.
As for Merrill, we've been focusing on her looks and mannerisms and now I'm realizing thats only part of it.
I'm reminded of an episode of Deep Space Nine where Bashir cured a woman who had been unable to interact with the world, she was aware but very passive. Bashir fell for her as she emerged from that state and started to date her because he was feeling very lonely at the time. Eventually he realized that she was going along with it as best she could out of gratitude and a sense of obligation, not romantic interest. Thankfully, Bashir felt horrible about taking advantage and ended it.
Merrill is isolated, exiled from her clan and you're one of the few people in Kirkwall to actually show her kindness and you're this hero. I get the feeling that she's with you because of how all of that distorts her views. Its especially reinforced by the fact that she still spends all her time in the Alienage working on the mirror even after she's moved in with you and she won't move the mirror in even if you offer.
All that combined with her smallness and innocence drives the point home for me over and over.
If it doesn't read like that for you, great. I wish it didn't read like that for me because I really like the character otherwise.