I think the fact that you are losing the hope that T could ever be anything else to you other than a Therapist is actually a good thing. It's a good thing losing that hope because it leaves room something far more precious and needed and that is grieving. The hope you have has kept you from acknowledging the full reality of your painful situation and therefore stopped you properly grieving the loss of the "good enough mother." The loss of hope is actually you transitioning into a new phase of your therapy.
It's the stage i'm at too. I recently went thru the same realisations as you, and i can actually say that i have found a little bit of peace in not chasing that dream anymore. It actually doesn't hurt as much as it used to. And the road that leads you back to yourself is going to be amazing, because by the time you get there you will be in full possession of yourself, it won't feel like a loss to get there and it just be you, it will feel like finally you have peace, finally there's no bitter disappointments when someone can't be the mother figure you want. You'll have control over yourself, there will be no more yearning for something out of reach. You ARE the prize.