At this point in "Twilight," Bella is in the hospital because of her encounter with James at the dance studio. Edward saves her, but her body is broken and bruised. Edward and Bella are discussing her mother's offer, to Bella, of moving to Florida. Edward tells Bella he is surprised that she declined and still wants to return to Forks. Bella says she wouldn't live in Florida, because Edward wouldn't be able to go outside until the night time. It is always sunny in Florida, and his skin would keep him from going outside. Edward responds to her that he wouldn't move to Florida. He would remain in Forks or somewhere similar to Forks. He explained, "Someplace where I couldn't hurt you anymore."
At this statement Bella begins to freak out. Her heart rate jumps, and she feels emotional pain that is stronger than any of the pain caused from her injuries. The nurse comes in, assumes that Bella's pain is from her injuries and tries to give her more pain medication. Bella refuses. The nurse leaves the room, and Edward immediately tries to calm Bella down. She begins to beg him not to leave her and makes him swear that he will remain with her.
After Edward promises to say as long as she needs him she begins to calm down.
"'Better?' He asks."
"'Yes,' I said cautiously."
"He shook his head and muttered something unintelligible. I thought I picked our the word ' overreaction."
"Why did you say that?' I whispered, trying to keep my voice from shaking. Are you tired of having to save me all the time? Do you want me to go away?'"
The "overreaction" that Edward was probably commenting on was the way Bella's physical reaction to his statement of not moving to Florida and not hurting her anymore affected her. Edward is constantly amazed at the things that upset Bella and the things that don't. He may have said something on the lines of "Why is she always overreacting?"
Bella and Edward have a complicated relationship and often Edward makes remarks that seem out of place to her, because he comes from a different period in time. He is so Victorian in his moral stance and his value system that this often causes confusion.
Hope this helps.