Just to add...Specifically, I worry about the uncontrollable changes that come up in life. I will age, there will be younger, beautiful women out there. I can get sick or injured. I will not be as desirable as time goes on and Sex is no longer as exciting as it was in the beginning. New Husband might decide he does not want to sacrifice monogamy. So yes I worry about my changes causing him to change and perhaps wanting more. And I worry about how these changes contribute to impermanence of a marriage or infidelity. In my fantasy, marriage withstood change. But it really doesn't.
JujuB,
I'v got two points to make. First, some of the things you're worrying about you can't really control. You could die in a car accident tomorrow, but worrying about that today is a useless exercise. Second, it's possible to get better as you age. When I was 51 I ran an ultramarathon. I ran the full distance, I never walked, and I finished with a very good time. I couldn't have done that when I was younger. We old folks can kick @ss, it's just that most of us choose to be old.