Mary, have you set any goals for yourself that have nothing to do with him and/or codependency? You say you exercise. Do you have a challenge or a goal you've set for yourself?
This winter, I decided to learn a sport that really scared me and was hard for me. I did it because I knew that while I was participating in it, I was only going to be able to think about what I was doing right then. Even if it was for just an hour or two a day, it was an hour or two of pure focused thought. Then it became really fun, but still pure focused thought. After that, I set another goal with another sport (riding my bike). So I have MORE time each day and week where I have this break from thinking about him. It's scary to ride in traffic; that one hill is really hard; I go farther all the time; I get stronger. Each day, I spend more and more time focusing on me in a good way - like how much I'm progressing - and less about him or me in a bad way (my codie issues, why he didn't try harder for us etc).
I'm not at that point of forgiveness. When I think about him, I'm either sad or angry. But like you, I just got tired of thinking about it ALL THE TIME. So I got busy with other things and I figure, with time, once I've really worked through all the anger and bad feelings (a little each day or week, not all day every day), I'll be able to forgive.
For now though, I'm just trying to get through it in a healthy way, which is to maintain balance and give myself (my heart and my mind) a break from thinking about why I did this and why I didn't and why he did that and and and. It's exhausting.