this is reality (there are no happy endings)
There's a difference between the stories Draco was always told about his Aunt Bellatrix and what she really is.
For a while, all he knew was the woman in the stories his mother would tell. And that woman sounded wonderful. But Draco never understood why, when he would ask if he could meet her, his mother always got so sad.
As he grew older, he began to piece together the truth.
Death Eaters.
Torture.
Insanity.
Azkaban.
When he finally gets to meet her, it's nothing like he thought it would be.
He expects the woman his mother told him about as a child - beautiful with thick, shining hair. Of course, he didn't expect her to be exactly the same after so many years in azkaban, but what he pictured is nowhere near what he gets.
He had no idea she would be so...unhinged.
Remember me, Draco? (I haven't seen you since I was a baby.)
Your mother says she's told you stories (yes, and they were quite different from reality.)
about all I've done (but now you're just a shadow of the woman in the stories.)
Of course, Draco never verbalizes these unsaid thoughts, not to his aunt, his parents, anyone. Because if he does, he won't be able to hold onto the pictures painted for him so long ago.
He knows the Bellatrix his mother mentioned is fictional. Even if she was there once, she is gone now. She doesn't exist.
But at the same time, he's not entirely ready to accept it.