Is it normal to think about an ex, even when the relationship was terrible?

I got out of a five year, very abusive relationship back in 2008. I've since moved on with my life, gotten married, had a baby, and have another on the way.

I dated my ex from the age of 16-21, and everything after the first year of dating was TERRIBLE. We fought constantly, it should have ended so much sooner than it did, but for some reason neither one of us would let it die. At first, he was just a prick, I'd try to control him, but when I grew out of that. A lot of my side of the fighting really did feel like self defense.

He started to use self mutilation as a way to guilt me. It was fucked up. Eventually he started telling me to sleep with other men and tell him about it, or else he'd kill himself, and after I'd do it, and feel shamed, he'd force me to tell him over and over again all the details. Then make me feel shitty when I was done talking about it. Then he'd make me humiliate myself by standing naked in a park at night or insulting me constantly. God, why didn't I stand up for myself?

I guess my question is: Is it normal for me to think back on my past relationship and wish I had done something sooner? Like, wish I could travel back in time to stop myself from staying so long.

But also, is it normal for me to wonder what my ex is doing now, and if he's with someone new, and if he's doing the same things? Or if he's treating someone better, and why couldn't he treat me better before?