This is something you've thought long and hard about, tiredlady, and you're doing it for YOU - your happiness, your health. I don't see that telling him beforehand accomplishes anything but stirs up another hornet's nest of drama.
Just curious: Why do YOU think you should tell him? What are you hoping his reaction would be? These are things I always ask myself.
You are not dying nor flying to Neptune - you are simply taking up another dwelling, something you feel is best for you. It is only as permanent as you wish it to be.