I'm not the best person to advise on this because I'm VERY attached to my T, but the attachment isn't as desperate as it was. What has helped me is this:

Talking to my T about the feelings, no matter how embarrassed or ashamed I feel. I always keep them in the open so they aren't festering in some secret part of my brain and becoming a private conversation with myself. Talking really does help as long as the T knows how to handle the feelings and doesn't shame them or try to avoid them.

Keeping in mind that T will never be my mother. I know that's desperately painful. I know it's agonising. But accepting that reality has been key for me. For as long as I keep hoping - even subconsciously - that she will one day let me move into her home and treat me like her daughters I won't be able to move forward. I need to remember that although my T is lovely and cares about me very deeply, there's a certain amount of acceptance that I need to reach as part of my work with her.

Being compassionate with myself always. This means that if I can't accept that T won't be my mother for now, that's okay. My T modelled this when I texted her once and told her most emphatically that I was NOT ever going to stop hoping I could live with her, she replied 'Okay, so don't stop hoping.' This approach might not work for everyone but it helped me because I felt she was accepting how I felt no matter what. That's been key for me. It has helped me realise that even though she can't be my mother, she's here for me and accepts me unconditionally in a way my mother never did, and while I can't see her ALL the time, I can get some of my needs met by her.

Eventually, over time, you CAN learn to start taking in what your T gives you without being traumatised by the whole experience. It's not easy and doesn't work for everyone. Therapy is an art not a science. I can only speak from my experience from what has helped me. I can't pretend to know what your process looks like. I just wanted to give you some hope that healing is possible. I haven't fully healed but I am much stronger. It boils down to a great T and my own desire to move forward.