Here’s what I might do in your situation:

1) I would tell T1 that I’d like to take a break from therapy for the time being. I’d ask if it’s possible to return at some point in the future. I’d frame it as I just need or would like a break to figure some things out on my own (or to focus on other things in my life or whatever) but that I’d like to keep the door open for returning if that’s possible, if that would work for them, etc. I think people taking breaks from therapy is a common thing and you don’t actually have to ever return.

2) I’d discuss my fears centering around the end of therapy with T2. Maybe not right away but maybe when I feel more comfortable doing so. It’s probably advisable to discuss the ending of therapy at the beginning of therapy even if that ending won’t occur for many years as ironic as that sounds.

I wish you all the best!