Not a day goes by that I don't think about if what happened to you happens to me. We are going on 52 years with many challenges in growing up ourselves and raising kids. Now, it is heaven. If she passes, I must stay with gratitude for the amazing gift I was given.
My, and your, measure of grief, is the pain you have allowed her to avoid. It certainly was not purposeful, but I wouldn't want her to suffer what I (you) are suffering now. We are each other's life, and I wouldn't want her going day to day in this kind of anxiety and grief if I passed first.
Dating? It's useless and hurtful in most circumstances. No one will ever "get" me like she does. No one will ever tolerate my cornyness or philosophizing like she does. My kids and grands will be devastated and supportive, but I will try and comfort them. I won't give them an extra burden of "What are we gonna do about Dad?"
Once someone is hete, they are never gone. Only their body, which dutifully contained their spirit and soul has worn out. You can still be with her spirit and soul every day. In parts of every day, keep doing what you did with her on tribute.
Many on these conversations talk about years and years of suffering and financial destruction with illness. It is said that a person who goes suddenly is spared illness because they lived a good and spiritual life.
This is a difficult one: Look inside yourself for who you are and genuinely always were. Who was it that she loved? You. Lucky you. Looking outside will wear you out and at the end, no one can really save you, although authentic religious devotion may come close, or even succeed.
I feel your loss. I hope I can take my own advice when the future is now.