I too have gone through this same thing. I still miss the son I use to know but I am learning everyday to accept and love the new son I have been given. You need to give yourself time to get through the grieving process. I have told many people that I had to grieve the lost of the son I knew before I was able to move forward. Now that I have accepted it I find it easier to deal with him and his illness everyday. We all want our children to grow up get married and have a family. My son does not want that at this time either. This does not mean that he or your daughter will get married and have a family in the future.
Believe me when I say there is light at the end of the tunnel.