First of all Happy Anniversary!! A whole year of freedom and look how far you have come.
I tend to find these days, the things which I would expect to bring me great joy, sometimes bring anxiety too. And I am learning that is ok, the anxiety tends to pass. Then the fun can begin.
I think its perfectly normal to feel the way you are feeling, and there are many potential reasons for it:
1. The mourning of the life you could have had if your Ex had not come along.
2. The fear that after all this time, he might come back.
3. The fear that you will somehow regress back to where you were a year ago emotionally.
Hope this is helpful, with only being close to my half year anniversary, I am not sure I am much help.
Big hugs
J x