ADD and Exercise

I'm fairly certain that my husband has ADD, although he insists that he does not.  Apparently during his first marriage, his first wife made him go get tested, and he was told that while he was close to the diagnosis, he didn't have it.  He thinks it's a made-up disease used by people who want to control others.

In spite of this, and in spite of our different temperaments, we have managed to learn to accommodate each other in most areas.  The one area where we cannot find common ground, however, is exercise.

I am a very disciplined person, and until about six months ago, I exercised daily and loved it.  My husband was slightly overweight when I met him two years ago, and since then has gained about 40 pounds.  He says that he feels terrible about his weight and wants me to help him do something about it.  He says that he wants me to nag him about exercise.  But when I nag him, he gets defensive and talks about all the reasons he doesn't have time to do it.

He gets angry at me when I exercise on my own.  He says "It must be nice to have time to do something that YOU want to do", and claims that he never has any time to do anything that he wants to do.  Because of this, I stopped exercising on my own and would only work out when he did.  The one time he caught me exercising on my own, he was furious with me and we fought for three days. 

I am feeling so frustrated, because a) I am worried about his health (he had a grandfather who died at the age he is now), b) I feel as if he is asking me to be responsible for his well-being, and c) I am frustrated that I no longer get to do something that I enjoy.

Is this typical ADD behavior, or is this related to some other issue?  Is it reasonable for one spouse to expect the other to nag them?  Is it reasonable to ask one spouse to only exercise when the other wants to?

Thanks in advance for your insights!  :-)