Absolutely DO NOT feel guilty. What have you got to feel guilty about? You did not create his health problems, his bed sores, his loss of control and dignity. He is making a rational decision, as did my GM - she refused all food and drink when she could see the way the land lay.
RThe nurse was being quite ridiculous. UNless she is blind and daft, she can surely see why he feels his life has come to an end in any meaningful way.
Is she implying that there is something you might do about it? Does she really think that there is anything that you or anyone else can do other than make him comfortable?- and that is her job, so if anyone should feel guilty, it should be her. There is no need at all for people to have bed sores like that nowadays. Good professional nursing should see to that.
My OH's life is gradually becoming less and less meaningful, in spite of a loving family and every medical help. His quality of life is very poor, not because he is bedridden, but because he feels dreadful for all but small windows of time, and his anxiety levels are crippling.
There does come a moment when all of us are likely to have to ask ourselves whether we or are loved ones have meaningful lives any more. It is not anyone's fault - it is just life's reality.
Hold your head up high, ditch the guilt and save your emotional energy for getting through each moment of this sad situation. My heart is with you. 