In spite of the years of pain and resentment and bitterness and whatever other emotion you want to bring out, it is STILL the death of a dream and the death of the life you thought you had or would have. I believe that mourning is not only appropriate, it is necessary before you can truly move on.
I was with my ex for almost 25 years; I filed on March 2 of this year and the final mediation is set for November 30. Even though my life is light years better than it has ever been before, I still feel sad that he is so sick and lost and that our kids and grandkids will probably never know what it is to have a father in any real sense of the word.