My bestfriend is talking to my ex. And it makes me feel bad or idk

Please tell me if I am not just over thinking things.
A bit of context.

We dated for few months. It ended badly. He wrecked the whole squad. Insulted me, insulted her, insulted friends. Blamed her for spreading lies about him ( she even cried because of it ). Made me feel so bad I was actually sick.
But we all decided last year that we have had enough and he was out of our life. We all told him we forgive him for whatever he did. And we are sorry if we harmed him in any way.

He also told me that he liked her at first and would have dated her if she had wanted to.
Which I told her.
And right after we decided that it was over, he posted a lengthy essay on how she was the most important person he met that year using a nickname pertaining to her.
[ he told me it was about me. And his friend told her wtf that was about you I helped him write it ]
Which again, I told her.
I tell her everything.

She just told me she talks to him now because a year passed, and it is alright now and that he was a friend ( they only really knew each other because of me ) and asked me whether it bothered me.
I said that it frankly did a lot, but that I am in no position to tell with whom she should talk or not. To which she replied that she was not asking my approval, just an opinion, because he was a friend and she would be keep up talking to him.

Do I even have the right to feel bad about this ? I don't even feel bad about him.
I just feel really disappointed by her.
Idk, like I feel betrayed for some reason ?
Am I over thinking this and should go for a walk and be less of a drama queen?