I have huge attachment issues with my first T and I am choosing to terminate for many of the same reasons you identify in your mutual termination. I can relate to what you say about your T's boundary issues, and I think that is where most of the damage was done for me. Long story short, I f***ing love this guy. I have to leave because a boundaried relationship with him hurts me over and over again.
I am lucky because I have found a good T to work through the indescribable grief of losing him. There is an aching void that can't be filled by a new T but I think the grief is something I have a chance of healing from.
I'm sorry you are going through a similar loss. I think the uniqueness of the relationship intensifies the pain.