In a Relationship with a Married Man/Woman?

I'm often asked for advice by people who are dating someone who is married. Forget the reasons why and how you got in this kind of situation, but now that you find yourself in it and you realize how miserable it is making you, what do you do? My most direct and simplistic advice is to: Tell them to get a divorce and give you a call and hopefully you will still be there.
In the meantime, get about the business of moving on with your life so you at least have a chance of having the kind of relationship you deserve. By putting your life on hold for someone who you can't be with, you miss out on living.