I agree - there is no "have to."

There are only "shoulds."

J (my T) is contacting the NASW call line for advice for his own sake.
I do not think anything is going to be reported as I have made it abundantly clear that it's not what I want.
Even so, I'm going to go ahead and tell them both everything -- starting with J -- so that they can have their own clear consciences or whatever and so that we never have to have this debate again.

Ideally, we will move on from that with them leaving the ball in my court -- I would just like to process it all and heal. And, if I cut S out of my life completely, I want to be the one to do it. I don't want it to happen because my T reported him and he's angry at me. I want to be in control of this. Not anyone else.