Am I overreacting?

So my boyfriend recently moved out (I still say boyfriend because he’s calling it a “break”) he’s staying with his friend and his friends fiancé. His friends fiancé has been my best friend since we were freshman in high school. She and her fiancé decided to keep it secret that he was staying with them. I had no idea where he went. And honestly I didn’t ask her. All I did was tell her what happened (and he and I have been great, it was truly a surprise) and she left me on read for 4 days. Then I found out he was there and asked her if that’s why she’s been ignoring me. She said yes because she’s in an awkward place because we’re “both her friends” and she doesn’t want to be in the middle. Ummm you’re his friend even though you pushed me to leave him on multiple occasions because he’s a “piece of shit who doesn’t deserve a family” ?? Hmmm. And then she said “I don’t know what he’s told you so I don’t want to slip up and tell you something I shouldn’t” so also keeping secrets for him? Hmm. We have two kids and have been together 6 years. Over those 6 years, she’s only actually been around him 3-4 times. But yeah, they’re such great friends 🙄

Am I wrong to be angry with her? No one asked her to pick sides but she did it anyway. She also knew for a month he wanted to leave and let me believe we were fine because it “wasn’t her place”.

For reference, My friend and I are 23, my boyfriend is 31.

I haven’t actually told her how angry I am. I don’t want to say something I’ll regret.