I had a horrid time with these thoughts too, the abandonment thoughts more than anything. It really is hard work and at times it felt hopeless. I think that was me struggling to trust, struggling to let her in, struggling yo realise that she did want to help me. It took months bit I finally do believe it and the dreams of abandonment have mostly subsided. In my case they made way for others but it is all progress.

I thought, from experience, that I woukd struggle also with the longings that you describe. The fantasies and the dreams for T to be my Mum. I didnt and still dont. I think what really helped me was that my T met my needs as best she could as my counsellor. By not holding back, she has helped to reduce these feelings to a level at which they can be explored by me, and in time, by us. If she had held back from these things then the cravings for it would only rise in strength to an unbearable level, a level at which they cannot be explored subjectively.

Does your T meet the needs that you have, those that she reasonably could be expected to as a professional therapist?