Is this a recent problem? Were you and the wife much more sexually active early in marriage? How old are each of you? Could it be she's older and possible a hormone issue? Could it be something in your attitude, behavior, or appearance that now turns her off? Is there a cultural issue in play?
When the debate is lost, slander becomes the tool of the loser. Socrates always time for a visit to a good counselor!
Sorry to hear about the condition. What has changed over the years? Look back and see where the fire/excitement has gone.