Best friend and room mate has been talking about me to my ex. Should I be upset?

TL:DR Former room mate and long term friend has been telling my ex the juicy gossip about my life. I feel betrayed. Am I am over-reacting?

I (35m) was living with BFF(34,TF) for two years during the pandemic. We’d been friends for 20 years and the living arrangement mostly worked. BFF became close to my partner (X,37) as BFF began to transition from male to female. X developed many friendships with my peer-group while we were dating.

After X and I broke up, I asked BFF about a month in if she had heard anything from X and how X was doing. BFF more or less responded she didn’t want to get caught in the middle. I thought that was sound logic As I moved on from a long and intense relationship with X I did all the normal rebound/crying/emotion venting that accompany it. BFF was there as a friend for me through all that.

I recently ran into X at a large party. I was probably a bit more cold than I needed to be but we greeted each other briefly and things were fine. At the end of the night multiple comments led me to understand she knew more about my life than she should have, like information about my messy rebound fling and other details about my life that don’t really affect or concern BFF. I spoke to a FR (F,28) , BFF’s current room mate, who mentioned BFF tells X all about what’s going on in my life, and all the gossip about my life.

I feel a bit betrayed. BFF understood not to put herself between X and me but then did some in a one-way flow. I spoke to some other mutual friends who all said they don’t really talk about me to her and she doesn’t really ask , beyond really basic 1-2 sentence summaries (He quit his job and got a new one, he’s adopted his dad’s cat, etc)