IME, exes tend not to be excellent sources of information about people. The reality is that you don't really know about the state of another client's attachment to your T or what his schedule currently is.

Even if you were correct about all the things you think you know, your behavior of "claiming" your T's office was really entitled and inconsiderate of his other client as well as your T. If I had to have my appointment in an office that wasn't his, because of some angry client who was squatting in it and refusing to leave, it would be a weird session. The new environment would be unsettling and I'd be wondering and worrying about the other person. Did you ever consider the effect you had on the other person?

Anne