My ex situationship added my best friend to her close friends list.

Hey! So I've been thinking about this since I found out earlier today and I'm not entirely sure what to think/do. For some background context, this situationship ended in September however she's been completely horrible to me in school ever since (laughing when I walk by, staring at me all the time, etc) and I've had to report her behaviour COUNTLESS times.

My best friend, who I will call Sara, told me that quite recently my ex, who I will call Monica, has begun messaging her on Instagram. It'll usually be replying to her notes, sending her reels, etc. I found it very odd the first few times it happened and I was really upset. Sara obviously noticed and gave me a weird reaction when I got upset.

Sara always says she dislikes Monica a LOT and continuously makes fun of her however she still messages back and conversates with her. I told her to just unfollow Monica or to message her saying she doesn't feel comfortable with the messaging considering what had happened between me and her.

The issue lies with the fact that Sara has severe anxiety and a huge fear of confrontation. Knowing this, I tried to simply suggest unfollowing Monica first however Saras excuse was "no that's awkward". In all honesty I got pretty mad at this and didn't really speak to her for a few days. Now, I'm feeling almost the same.

She told me today at around 12 that Monica added her to her close friends list and showed me the pictures she was posting on there. I laughed along because the pictures were weird and then went silent because I felt weird. I just got out the shower crying about it because I honestly feel like Monica is doing this as a way to get back at me or idk. It feels like she's stealing Sara. It lowkey feels like my own best friend is betraying me in a weird cryptic way.

So, WTF do I tell Sara and how can I somehow convince her to unfollow Monica without her getting annoyed by me for being upset about this?