I'm not with the crowd on this.
I do think Edward has realized how much he hurt Bella. But I don't think anyone can really say that he was worse than she was.
By the time Edward and Bella get home, Edward has already figured out that Bella isn't quite right. He doesn't have the reason. It isn't until later in their discussion that he learns just how dead she's been. He thinks she doesn't want him to kiss her because she has moved on like he wanted her to. Then he finds out that she thought he wanted to die because he felt guilty, that she is terrified of her feelings for him because she's afraind of him leaving again, and that his leaving her is worse than the werewolves, Victoria and the Volturi -- because any of them could kill her, but he could leave her. Then, after all that, he finds out about the her hearing his voice when she has the delusions. When he realizes that the reason she's been into risk-taking activities is so she can hear his voice, he's floored. He isn't stupid. He knows what he's done.
Now, for the dueling depressions:
Neither Bella nor Edward have dated others before. Edward, however, has livednearly 110 years (the last 90 or so of them with 24 hour days because he doesn't need to sleep). He has a lifetime of experience to draw upon to deal with the ramifications of his choice to leave Bella. On the other hand, Bella has 17 years of experience to draw upon. Not nearly so much. And her family isn't as stable a support system as Edwards has been most of his life. She has flighty RenÃƒÂ©e, who needed Bella to be the adult, and Charlie, who is pretty non-communicative. He support system, when Edward chose to leave, was mostly his family -- and he took them, too, even if he didn't stay with them.
Now, if you know about clinical depression, there's an easy and a hard way to deal with it. The easy way is to curl up in a ball and ignore the world. Trust me, during a depression it is so much easier to just pull down the shades, turn out the lights and hibernate. The hard thing -- because it is fighting your body and your mind -- is to get up and function at any rate. It doesn't make the feelings go away, it just means that in addition to your feelings, you are doing all the things that need to be done, too. Bella takes the hard road. Edward doesn't.
As one of my friends said, "Rock bottome isn't wanting to kill yourself. If you want to kill yourself, at least you care enough to want something. 'Rock bottom is when you stop caring whether you live or die."
Edward wants to kill himself. Bella doesn't care if she lives or dies anymore.
Then there's the knowledge. Bella has lost her support system and the love of her life. She thinks Edward doesn't love her anymore. She has no reason to think he's coming back. She can't even think about the good memories because they tear a hole in her -- to have safe memories, she has to have him screaming at her angrily. She doesn't have her epiphany until he's back, so all she knows is that this is the only way for her to remember him without hurting herself more. Even after he's assured her that he's staying, she can't trust him to mean it.
Edward, on the other hand, knew that she loved him when he left. He wanted her feelings to dwindle so she could live a happy, human life, but he wasn't rejected by her. He knew she was in forks, He knew that if he made the choice, he could go back. Bella didn't have that option.
They are both pretty low, but just because Bella is functioning it doesn't mean that Edward is worse -- he just appears worse because it looks so different from normal.