You miss her because you are remembering the good times, and you are forgetting the bad aspects of your relationship. You want what you can't have. You say you were "very unhappy," so I would honestly try to move on. Delete her number, and distract yourself with friends and fun activities :)
You developed habits and routines together. Change is scary, I am sure it is the security of a relationship more than her that you miss if you were unhappy with her. Work on strengthening your friendships, maybe find a new hobbie or join a sports team or something. Keep busy, try not to spend to much time alone at first. Focus on the possitive, don't dwell on your failed relationship. Learn from it and move on.
You were just used to her being around. Now there is empty time. Get back into life. Do things. Go out with friends. Involve yourself in some activities. Get back into the game and have fun. In time you will stop thinking about her. Remember, you broke up for a reason.
Sometimes it just depends on how long you were with her. Sometimes people just get used to being together. I don't know if your relationship was a good one maybe you loved her but if not, it is just attachment
There is another. And if you are both patient you will find each other. Remember no heart will be practical untill it can be made unbreakable. This is the time for you to learn to laugh again. Don't worry so much, your getting closer.
i think you are realizing that you weren't always unhappy with her and that you did have some good times and those good times are sticking out in your head and your remembering how it was but you have to understand that shes not perfect
You miss the stuff that was making you unhappy when you were with her. It is a normal reaction. You are missing being mistreated. It was a part of your daily routine and you got used to being unhappy. so now you miss it. Please don't go back to her because you said you broke up because she made you so unhappy. The one you love should make your life happier not unhappy. Move on. Run and don't ever look back!