When you break up with the guy or girl that was so bad Satan was taking tips, most of your friends are overjoyed. They throw a party. There's cake, there's drinking, there's not a lot of time for you to be sad.
My last break up was one that will honestly take a while for me to get over. I was devastated and furious with what happened after a 4 year relationship, thinking that me and him would last forever. I missed him for a few months, then I started to realize that I was better off without him, but who knew that I would miss him again; miss the hugs, cute nicknames, or dates. He was a jerk, I did and did not want to be with him again because he broke my heart in the worst way possible for someone to break a heart. I still reminisce about our times together, even when a song came on and remind me of him I would break down and hate myself for thinking about him. Why go through the struggle of missing him? Cry at the very moment when I hear his name?
Because he wasn't always a jerk. Our relationship was never unreal. When you first meet someone they're nice, they're funny, they're trying to woo you. It isn't until later that their true colors show.
And instead of saying why didn't I know they would turn out like that mourn the person you fell in love with. Mourn them, don't mourn the jerk who cheated on you or abused you or harassed you. Allow yourself to fully and utterly mourn the person you loved. It's okay. And it doesn't mean you want them back. It just means you lost someone you once cared for.
And I promise, if you do that, letting go of them and your relationship will be 10,000 times easier.