Petunia wanted to love Harry she really did, not that he would believe it, but she couldn't.
If she loved him, then it would hurt when the wizarding world snatched him away from just like it had Lily.
So made herself dislike him greatly, she made him aware of the dislike early on.
She had to save herself from the pain, there was a time when she thought he wouldn't be like Lily an maybe that he would be normal but that didn't last for long.
He wasn't normal, he would never be normal and like Lily he would embrace what he was.
Yet underneath the dislike, the hatred for what he was and measures she took not be hurt by having someone she loved snatched away and taken to a world she would never be a part there was a piece of her that loved him.
A piece she wouldn't or couldn't admit to.