I dunno if this has unlocked a lifetime's pain, and I'm mourning more than just this relationship.

I think this^ may be important, and may have been what your current T was trying to get at--though his words were clumsy and unfortunate. Of course you had a relationship! But your relationship with him was probably different (not lesser than, just different from) his relationship with you. Now that you have no interaction, neither relationship can evolve. So, in a way, you are stuck in time emotionally. I think over time your perspective of the relationship will change in some ways. Working through your feelings--especially the aspects that originate within you-- is what will lead you to accept with a sense of peace your feelings and the more objective reality of the relationship equally. I would hope that your T would help you move through this, rather than leap frog over it by dismissing it.