It was a type of grief for me to come to terms with my new reality and nearly 3 years after my diagnoses I am starting to get there. I had to give myself the time and space to grieve the life I used to have.
It is, indeed, a kind of grief for us. There is great loss in a person's life when fibromyalgia hits. The losses are different for each person, but they are always large and meaningful and difficult to accept. The key to managing it effectively is acceptance or, as you say, coming to terms with what is reality now. This I think is the most important thing.
And yes, it takes time. Three years to be getting there is not at all unusual. I actually think it is an ongoing process, at least for me.
I am a person who has practiced acceptance as a way of living for many years, and before I developed fibro. I have had fibro for years now and have accepted it to a large degree and count on that acceptance to make it possible for me to live with it. But I still have days when I do Not accept it! And instead want to rant and rave about it, I get angry, and so on. I think most if not all of us never reach a point where we are all done with that work and are 100% accepting of it all the time.
Part of that is, as you say, giving oneself the time to grieve what is lost and to come to terms with it, and this takes time. Sounds to me as if you are on track. Welcome to the forum.