Hey there,
I totally identify with much of what you said. For the first year after my xabf and i broke up, i was asking myself the same questions and feeling like a grade A idiot for allowing him to take up any space in my mind. I would recycle old conversations, imagine the showdowns i wanted to have in the future, and look back with total disbelief about what happened and how someone could treat another human being this way. All I can say by way of help, from my own experience, is that time is a great healer and to be patient with yourself in allowing that process to work. It isn't like a normal breakup, and if the A is unwilling or unable to engage about their behavior, you're left holding the pain of two people. But it does get better with time. Other things I found helpful -- trying to have no contact with the A (or the A's friends), as much as you may want to; exercising on a regular basis; and doing some traveling to get away from all the muck. Hang in there...