I understand where people are coming from when I say that, but the truth is that Edward and Bella's relationship wasn't exactly normal, was it? By the end of Twilight/beginning of New Moon, I'm pretty sure that Bella thought that Edward would be in her life for forever. Edward was her first love, and she never doubted for a second that they would be together and stay together. Wouldn't you be shocked, upset, completely heartbroken if you were told just months later that the love of your life was leaving you, saying that you're not good for him and telling you to just forget about him because it'll be like he never existed? That, coupled with Bella's personality, makes her reaction not so unbelievable. Everyone is upset when their first love goes bad, and I'm pretty sure that there's nobody out there who wouldn't be a bit off it the love of their life just up and left one day. She's pretty much romantically immature at that point, so it would come as a huge blow to her. And the break up was completely out of the blue. Of course she's going to miss him - he took away every picture, every memory, every single thing that would remind her of him. Even in reality, some people just can't deal with bad break ups.