Hating someone your whole life is great in movies and video games, where the hater uses their drive, intelligence, resources and lack of concern about any consequences to pull off some really amazing revenge. But in the real world, I think most of us aren't willing to go to the lengths needed to properly pay our hated back to someone. So if we can't act on our hated to the level we feel they deserve, then the only person who would suffer from that hated is the person caryring it around, day after day. Of course, never forget what they did, you don't want it to happen to you again, but forgiving isn't about letting them off the hook, it's about allowing yourself to start feeling good again.
That being said, feel however you want to feel, I ain't the feelings police. But that's how I see it.