My friend is romantically “talking” to my ex husbands brother (currently going through a divorce)

I have been going through a nasty, draining and toxic divorce for the last year. It has taken a toll of me mentally, physically and emotionally. This “friend” knew all of this. 3 days ago she received a Facebook request from my ex brother in law. She didn’t know It was him until she saw my ex in pictures with him. I told my friend he is married with 3 kids. She said that he stated he’s getting a divorce. I expressed that It makes me uncomfortable especially since I’m in the middle of this nasty divorce. I was supposed to go out with my friend group tonight but found out he’s going to be there. So i asked her about It, she said “I know and I’m sorry. But i really like him. Come out and don’t talk to him.” I said I have worked to hard to get to get to this point in my life and away from anything associated with my ex husband. She said i hear you but i think he’s coming. Again, she has known him for 3 days. It’s clear to me that we aren’t truly friends and doesn’t seem to care about how i feel. So I decided to stay in and i feel defeated. I would love some advice. Thanks!