That does sound very bleak when you put it that way. From your description,
you seem to be going through a grieving process. Many relationships have a natural lifespan. Is it possible your marriage is reaching its final days? Have you considered counselling to help cope with these changes?
I tend to agree that the secret to happiness lies in expectations, but I prefer the adjective "realistic." However, that can only take you so far. Sometimes you need to hit the reset button and try a whole new approach.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker