Here's what Stephenie Meyer has to say about Edward's tragic flaw in Eclipse:
Edward's big mistake is overreaction. It's in his nature to be too extreme… When he sees the error of his ways, he goes too far in the other direction. He could have chosen a middle ground – maybe admitted to his jealousy and asked Bella to choose him, rather than watching her get in deeper with Jacob. Of course, he has other issues that make forcing this issue problematic. What if Jacob is better for her?… Should Edward really insist that Bella give everything up for vampire life? (source)
Edward's extreme personality surfaces in Eclipse in two Edwards: Edward, the great manipulator, and Edward, the "patron saint of ethics" (24.13).
Edward, the Great Manipulator
When it comes to the subtle ways of manipulation, Edward has them down cold. Pun intended. His first work of manipulative art is when he persuades Bella and Charlie that Bella should take a plane trip to see Renée for the weekend, because the tickets she was given will soon expire. Later it turns out that he wanted Bella to leave town because the Cullens and werewolves picked up Victoria's trail around Forks. Nice work, and forgivable since he acted out of concern for her safety.
When Edward and Jacob announce open competition between them, though, he steps his talents up a notch. To Bella's surprise, he professes to have given up on his werewolf prejudices and that he trusts her to be safe with Jacob. Of course Bella believes him and makes a show of Edward's tolerance and selflessness around Jacob whenever he openly expresses his dislike and jealousy of Edward. Her drooling over Edward's perfect ethics prompts Jacob to shoot even sharper daggers at Edward, which in turn loses him even more points with Bella. Smart move, Edward. Very smart.
It's only when Bella, Edward, and Jacob huddle up in the tent together with a snowstorm raging outside that Edward seems to lets his guard down. In his heart-to-heart with Jacob, he openly admits to his jealousy and that he keeps playing the nice guy, because it scores points with Bella: "I'm not such a fool as to wear [jealousy] on my sleeve… It doesn't help your case" (22.121).
It does help Jacob's case, though, that Edward mentions their wedding to Bella within earshot of Jacob (deliberately trying to hurt him). Guilt-ridden, Bella agrees to kiss Jacob, which makes her realize that she's in love with him too. That scenario Edward surely didn't intend but, again, his manipulation skills help him skew the situation in his favor. Not only does he tell Bella that Jacob is the big manipulator here, because he told her he'd kill himself if she didn't kiss him, but he selflessly forgives Bella for her transgression. Again, his plan works like a charm: Bella tells Jacob: "He wasn't even mad at me – he wasn't even mad at you! He's so unselfish it makes me feel even worse!" (26.134). No need to mention that Jacob accuses Edward of being the better liar, which, in turn, causes Bella to wonder about Jacob's lack of ethics.
So, in short, some very skilled manipulative work here, Edward.
Edward, the "Patron Saint of Ethics"
Of course, we could also be a bit more on the trusting side, like Bella, and give Edward the benefit of the doubt. Some of his actions do seem to be selfless, after all. He always has Bella's safety and happiness in mind, even if that means skewing reality a little bit to keep her from worrying. He also seems to acknowledge that Bella is in love with Jacob and that Jacob might be a better match for her. He goes so far as to say that if Bella wanted Jacob, he'd let her go. He even makes a big step in Jacob's direction, saying, "You know Jacob, if it weren't for the fact that we're natural enemies… I might actually like you" (22.174).
Although he deliberately hurts Jacob when dropping his marriage plans with Bella on him in a dirty way, Edward seems to be genuinely concerned when Jacob later gets wounded: "Edward fell to his knees… gripping the sides of his head… his face furrowed in pain" (25.81).
His concern for Jacob even warms Charlie up to him when he witnesses Edward and Carlisle attend to Jacob's injuries after the battle (a.k.a. "bike accident"). He tells Bella that Edward seemed as concerned about Jacob as she is, and that he acted like a brother to Jacob.
Edward's sweetly traditional views of marriage as a sacred commitment to eternal love, and his concern about protecting his and Bella's virtue also speak to his benefit. We get the feeling that, though he battles with jealousy, he strives to be selfless for Bella's sake.For more info on Edward, check out his "Character Analyses" in Twilight and New Moon.