No Rest for the Weary

I don't even know where to begin. I guess I thought that I could 'do' a relationship. I mean, I was in one for over 12 years, so how f-ing hard can it be to start over?? Oh, HA, I am an idiot-I am well aware of this as I type that.
I have no idea what I'm doing. I *think* that I do, and for days on end, the results of my efforts are wonderful: shared laughs, sweet smiles, warm feelings in the very center of my being....
...and then, I don't know. I become afraid. Afraid of hurting him, afraid of being hurt, afraid that I am falling too fast, afraid that I will open up completely and will be torn apart again.
So I squash those feelings.
But they keep resurfacing.
And without realizing it at first, I am becoming defensive. My walls are going back up, after I have let them down with such ease. And I don't know why.
Now I am doing damage to a relationship that is still new. I am acting a way I do not want to act, that is not part of my personality, and it is out of fear.
I am my own worst enemy, but fear is making a run for my money.
And the fear is making me withdraw again. From the life I so desperately want and deserve.