I have abandonment issues as well from my mother too. So they are very deep and I don't see them changing all that quickly because of how deep they are.

That said, I have learned to trust my shrink and know very well he would never abandon me. I've even tested this out and found it out for myself.

Perhaps you are trusting your therapist more and then the old feelings of fear are coming in to protect you? In other words, even though really difficult and painful, perhaps there is something positive in it in the sense that you are letting someone in, but having trouble really going with it all the way because you have these issues. And perhaps bringing up will give you a chance to get some relief and get a chance also to hear some reassurance that might help.