am i overreacting? my friend wanted my ex and im not over it

I know my friend was trying to talk to my ex but i can’t prove it

Okay, so me and my ex broke up after a year. we both have this mutual friend that he’s known for a while since they went to elementary school together but I’ve only known her since the beginning of high school. I am INFINITELY closer to her than he is and they really did not talk that much before we broke up.

All of a sudden after we stop dating she just keeps talking about him and bringing him up. I talk about someone else with his same name, she circles it back to him.She would text me about what he’s doing in the class they have together . She started putting stuff about him in her notes. SHE POSTED HIM ON HIS BIRTHDAY FOR THE FIRST TIME EVER (it was an off guard picture she took of him just walking in their neighborhood 😐). In one instance, i watched her yell across a room to get his attention as he was leaving and say hi and then size him up as he walked out the door. She told me how he didn’t come to class one day cs of a sports incident and how she called him in the middle of class to check on him.

Obviously all this is weird, but i never brought it up because i dint want to make a fuss over someone i was done with. Eventually one of our other friends got mad at me and told her that i think she was trying to get with him. She confronted ME and denied it and said she’d never do that. But it irks me so badly that i’ll never know because she’ll always deny it even though i 99.99999% know that she was .

Idk what to do cause it’s kind of eating at me that she would do that

Side note: this wouldn’t be the first time she’s talked to a friend ex, nor would it be the second time, or even the most recent time .

Am i overreacting for feeling like i need to know even though it’s been a little while? Am i overreacting because he’s an ex and i need to get over it ?

Edit: 1. when i say they’ve been friends, i mean acquaintances. They’ve only KNOWN each other for a while as in been in the same classes, they are not nor were they ever, close friends.Im not getting in the way of their “friendship”, because it is nonexistent.

2. This was an abusive relationship, and she knows that. Verbally, Mentally, and somewhat physically.