The baby is representing an inner need - in that sense, as soon as you begin to feel the need is met, you become terrified that it will be withdrawn. I think this must have been part of the dynamic between you and your mother too - that she would sometimes begin to meet your needs and then withdraw again.

Love, ****

I was SO scared that if I let go of T even a little bit, he would disappear

It is very abnormal in human relationships to form a close attachment, and then only see a person one time per week. Anyone who wouldn't understand this, doesn't understand the normal, human reactions that people have when in a therapeutic relationship!

I think it is fine to acknowledge the role a T has in our healing. (I owe my T a lot for that!) I don't see the two things you mentioned as being necessarily connected. Like say that together with another artist you painted a magnificent painting that hangs on your wall. If the other artist should move away, the painting does not disappear. It has been created and it endures. The changes you are making in your life (the healing) will not go away if someday your T leaves the scene (even though her absence is painful to contemplate right now).