I've had to detach myself from a few Ts. It was very hard but was doable because I had another T like you do. I spent many sessions talking about my former T. Have you talked with T2 about T1? I would think that's the best way. I attached to my new T when I switched each time.
One of my Ts always said it was unethical to see someone if they aren't progressing or going over new material, that just continuing therapy because you're attached or obsessed with your T wasn't right. After a certain number of years. I don't know if I agree, but if you aren't getting anything out of it, but you can't leave, maybe try cutting down sessions gradually. I know it's not easy. I don't want to think about leaving my T but I know she wants me to be able to.