I think I know what you mean, it might be also that you don't want it to end (don't feel right now able to imagine yourself with this ending), so that gives you extra anxiety and the constant focus on the fact that it will end.
I don't have any advice on this, apart from trying to accept it and maybe also discuss it with T. Also, as said above, maybe look for another T for after this, just as a safety backup plan to calm you down a bit. In the same time I hate endings too, so I can relate.
Schema therapy sounds good though, I think it's worth to stay in it.

I'm in therapy and it's not the best kind for BPD, though I think I would be lost without it. Also I don't know what will happen after the summer, in about 3-4 months I might not even be able to stay in this city anymore. So in a way I'm in a slightly similar situation.