What if a girlfriend hates her ex? How can they live in peace?

In your case, to put it mildly, you think differently. To put it bluntly, are you out of your mind Some people may think that they can still be friends with their ex after breaking up. Maybe that's what you think between you and your ex. However, your current one doesn't think so. Maybe your current girlfriend will think that after breaking up, she should be the most familiar stranger. Personal understanding, don't blame if you don't like it!