WHEW, OK a lot of emotion here. This may have been covered. I apologize if it was.
1) Your H has had a long ongoing affair 2) Y'all don't get along very well 3) He broke it off with the OW, but she is still hounding him.
Is he still seeing the OW? If not I would not get too upset about the calls and her purusing him. Since I have broke it off with the OW, I have gotten the full gamut of emotions from her. One day she will tell me she knows it's over and wishes me well. The next day she hates me. The next she loves and wants to do anything to make "us" work. It is very tough to break it off with the OW.
Your H probably feels "stuck" now. It makes him grumpy. You need to give him hope in your marriage. Not by what you say, but by what you do. The best way to change other people is to change yourself.
You seem to have a lot of anger at this situation. That is understandable. Anger is part of the healing process, but I think you need to let go of some of that anger. I can't tell you how to do that. Maybe others can.
Think of it this way, if you keep doing the same thing and get the same results...how can you expect change?
I do not know the depth of your situation, but I would hold off on divorce talk and thoughts. If you honestly get to that point, the lawyers will be waiting.
But you are leaving the door open for a divorce by even talking about it and pursuing it.
As far as Atkins. Man it worked for me. I lost 65 pounds and have kept it off. I do not stay on it 365. I will stick with it strictly when I see my wieght get past a certain point, then I will just monitor what I eat.
Hope some of this helps and I'm not too far off base.