I am happy for you that it went so well, everything you said sounds like a great fit, no matter how long you work with her.

As a thought on the "why is T okay with this", maybe reflecting your beliefs about relationships would lead to some increased understanding. I wonder if you grew up where people considered other people as possessions, and that if I had her as my __ , then you couldn't. Sometimes i think this happens kind of naturally in childhood homes where there is a lot of emotional neglect, so connection with people seems like a resource that's scarce.

My interpretation of your T is that she subscribes to the "if you love something let it go." Why wouldn't she want you to connect and heal with another therapist, whether she isn't available or otherwise? She doesn't want to possess you. She wants you to feel better and struggle less. There was a time in my therapy a few years ago that I was really struggling with something and saw another T for a single consultation without discussion with my T. I told him afterwards and talked about why, but he wasn't defensive in the least and had no issues with what I did and said I could go to anyone I wanted whenever I wanted and didn't need to say anything to him. Your belief that she wants to get rid of you, that's your past talking. Try listening to your present.