<human>: Can you provide a brief rundown of the text in within 3 sentences?

In May, my ex and I broke up and it was a NASTY break up. We fought a lot and he was extremely inconsiderate to me post break up- saying that he missed me and was thinking of getting back together with me, and I almost was going to agree to getting back together, but then in June he COMPLETELY ghosted me and I have not talked to him since.

BUT- since our break up, one of my close friends has gotten very close with him. In a way that is a bit uncomfortable- not in the fact that I still have feelings for him- but in the aspect where they are so close that other people have come up to me and asked what is going on between them. My ex comments flirty comments on everything my friend posts on social media, even some things that I have commented on. There are several instances where I have definitely caught my friend trying to hide the fact she was talking to my ex.
I really don't know what to do with this. It just makes me pretty uncomfortable and its starting to make me dislike my friend. Even though sure she can technically go for him, she knows how much he hurt me and treated me badly- so I just don't understand why as a friend she's getting so friendly with him. I don't know what to do- I don't even know if this is worth bringing up with her- but I just want to stop feeling uncomfortable.

Also as more context on my friend- she has previously blatantly hit on one of my other friend's crush, causing my other friend to no longer have a chance to get close to her crush. 

Any tips on what to do? It's gotten uncomfortable to a point where I'm not sure if I want to go to a party where they might show up just because I don't know if I'm going to see something I don't want to see...
<bot>: My friend is getting really close with my ex boyfriend to the point that many people are noticing and it is straining my relationship with my friend.