Okie, I totally understand what you are saying. In fact, I think you are very brave to join a group in which your T is the facillitator.
Just so that you know you are not alone, I will tell you that I have carried a fantasy since I started seeing my T, that he has no other clients. The thought of him interacting with anyone the way he does with me (especially if it is a female) is painful. Two sessions ago he mentioned another client for the first time ever. He told about a client who is a child, that he bought colored pencils for (the story was actually relevant to a dream I had that I had been telling T about). Inside I was thinking, "Who is this damn kid???" I didn't tell T about it and I felt like such a baby. Not only does he have another client but sometimes I want to be a child in Ts office. And this kid gets to be a child in Ts office.
It must have been really hard to see your T doing her T thing with other in the group. But the fact that she cares about you is not an illusion. It's real. And you still are special to her even though it is hard for you to see that right now. Because none of her other clients are the exact same person as you-- so even though she see other individuals, she cares about you individually.
I completely empathize with you.
I never told my T my feelings in response to him telling me about his child client-- I felt like an idiot because it's like I can't maturely handle anything he tells me. All the guy was trying to do was tell me a story and inside, I couldn't handle it like an adult.