The battle must be won in the mind--how you think about and perceive things. There are always roots to why we do things that just don't make sense. There must be some lies that you've believed (probably instilled in childhood) that allowed the connection to form so strongly with the abuser.
You probably maximized the "good" and minimized the "bad" while in the relationship. Just because you walked out, doesn't mean you automatically changed your way of thinking--you probably are still now doing the same.
The roots could be many things--it is different for each person. Perhaps it was a co-dependent relationship--where you believed some kind of lie about what you deserved. It could be a worth issue.
I think there might be some sort of fear issue. What is it that you are afraid of by not being with him? What are you afraid of when being with him? Fear attacks on both sides of the equation.
I think manipulation is really a big part of abusive relationships, too. I was in an emotionally abusive relationship and my ex just got me so confused because he didn't do it all the time--but he'd do it enough to make me question my sanity instead of questioning his. I believed that he must be right. I was so deep into it that I couldn't even see clearly.
My journey towards healing started with reprogramming my mind to think in a healthy way. Then there was inner-healing, prayer, and learning my true identity and learning to love myself (and others) enough to set boundaries.
Perhaps you don't miss your ex...but something that you got out of the relationship but in an unhealthy context.
Finding another "fish in the sea" until you deal with these issues probably won't help and you are likely to attract the same type of person until you change your beliefs about yourself and relationships and come into a place of healing and wholeness.
You can do it! Try not to go into past "shoulds" or future "what ifs" but live in the present. Deal with your own "demons" and then your next relationship will have a much better chance for success and healthy love.