Lucas wrote himself into a corner, that's why Padme dies. He finished two films and then realized that he hadn't set up Anakin's fall to evil, so when it came time figure out why a whiney, bratty teenager will transform into a bloodthirsty, kiddie-slaying lapdog of Palpatine, Lucas got desperate and went for the old "he loves his wife so much he'll turn evil to save her" routine. But then Lucas realized that if Vader loved his wife so much, the audience would expect Vader to go searching for her, even if he had become evil! Maybe he'd want to show his love by doing EVIL things to her instead of pornographic things, but nevertheless, Lucas was trapped. Padme had to go.

It would have made more sense for Anakin to desert Padme in his fall to evil, since wife lovin' isn't generally considered an evil act. Anakin and Padme could have just had an argument and Padme could have fled when Anakin started in with the domestic violence, like maybe after he jolted her with force-lightening.

Or Anakin could see the future and in it Padme would be laid out in front of a TeeVee like a beached whale, totally fat and stuffing her face with Bantha Rinds. Anakin confronts her and tells her he's leaving her for a hotter broad, and when Padme tells him she's pregnant, he says, "too bad, bitch, go get an abortion!" Then he force-squeezes her uterus in an attempt to kill her babies. That would be far more EVIL than how he loves her too much in ROTS.