Marriage/relationship question

We have descussed many topics on this board. Everything from births to death, weddings to divorce, windfalls to forclosure and the list goes on. I have a serious question and I want to ask my family here at FABO. I know every relationship goes through a "down cycle", a time when you are not as intimate as you once were, but when does it become not normal ? I mean, at what point do you say it has been too long and enough is enough ? There aren't any medical issue's proventing it, everything else is fine, there is just no intimacy.