Oh dear. This is so very hard, scary as you say, and also heartbreaking. Denial is protective. It eases as you accept. If Denial isn't keeping you from doing something important, there's no harm in it. Is there a caregiving support group near you, either sponsored by the Alzheimers Association or some other group? Listening to other 'well spouses' might help. Now that most everything is on zoom or some other platform, you can 'go' to a support group anywhere! There are also some excellent dramatic movies that are streaming these days. When I googled 'good movies for alzheimer's' there were a number of suggestions: https://alz.org.sg/5-unforgettable-films-about-dementia-you-need-to-watch/ is just one.
Surprised, shocked, fearful, angry. I'd be patient with yourself. This is a HUGE change. There are books, groups, movies. And your own wisdom. I would find a good therapist and even once a month sessions will help you learn how to be compassionate with yourself AND with your spouse. I am sorry. And you will learn so much. Not that you ever wanted to learn these particular coping strategies...