It is hard for me to read this thread for this is a road on which I have traveled. I spent 17 years in a marriage with the last 10 in near celibacy. And in my case it ended in divorce. Mind you, this was not the only reason for the marriage going south but it was one reason and a symptom. Because of this I am going to blunder into an area of discussion the others have only touched lightly.
Perhaps you need to take a long hard look at other aspects of your life with this man. Are you truly happy? You say separation is not an option. Take a long hard look at that statement. Sometimes we say things like that without considering the alternative. Consider other aspects of your marriage that could be improved. Consider why it is not an option to walk out of his life. Are you in a rut? Is there no alternative because the alternative is so scary? Believe me, this may only be a symptom now but the time could come when it is a towering obstacle to putting this marriage back together.