She terminated me and we are now friends but I cannot call her anything other than Dr. (her last name) when I speak to her. When I attempt to call her by her first name it feels oddly painful and I feel like I'm losing something. I don't quite understand why.

We've known each other for over 5 years and she's cared for me in a way no one else has (non romantically).

Why does calling her by her first name make me feel such a sense of loss?

She says she's been waiting for me to call her by her first name for years.

Any ideas would be greatly helpful.