How do i deal with this mental gymnastics ?

I’m genuinely confused and need outside perspective.

My ex and I are on decent terms now...(we were together for like 7yrs and i ended it because i got to know he was attracted and flirting with another woman over texts). We talk occasionally, share normal life updates.

Recently, while screen-sharing today, I noticed that the girl he emotionally cheated on me with is still sending him Snapchat snaps.

What’s confusing: She told me herself earlier that she’s done with him, called him an asshole, and said she wouldn’t talk to him again. Yet… she’s still sending snaps.

We both were school friends earlier but stopped talking dur to distsnce, not any such major reasons. So, once when i asked hef casually about my ex i got to know from her that he was flirting with her. She told me that she'll stop talking to him, called him an a**hole and we both had a fun laugh about it that we shouldn't fight and stress over a guy. She told me she'll block him but later said she couldn't because "blocking seems alot."

Now that me and ex are on talking terms, kinda trying to get back together. I find it hard to ask him directly that why is she still in contact with him. I mean he told me once that he is no more into her. But from her perspective, i find it hard to understand that why is she still in contact with him.

I mean, i am not against male-female friendships at all. And i can be wrong here too, idk. But i need some perspective on this.

I’m not trying to control anyone. I’m not asking him to block her. I just don’t understand the psychology.

If someone thinks a person is toxic and claims they’ve cut them off ....why keep casual contact like snaps?

Would appreciate honest takes.