<human>: Could you distill the essence of the text into 1-3 sentences?

My ex wants another chance to make things work, but I told him I wouldn't consider it if he is still talking to one of his friends (who also happens to be an ex of his). Normally, I would never give someone an ultimatum of "it's me or her" but this girl:

1. Threatened me on Thanksgiving, sending me a Facebook message that said "I'm so glad you're not dating [ex] anymore. If you ever fuck with him again, you should be really afraid, little girl."
2. Told him that our relationship was "sick" because there was a 6 year age difference. (I'm 21, he's 27)
3. Admitted to getting guys so drunk her friend could have sex with them, to the point where it sounded like she was assisting in rape.
4. Ignored both of us and talked to her neighbor when we visited her last summer. It had been months since my ex had seen her and she was pretty much a horrible host and completely disrespected the fact that we were only there for a couple hours before leaving to go home, 6 hours away.

She helped him out of an abusive relationship in the past, but IMO that does not excuse the terrible things she has done since then. She's said a lot more really mean things about me that I didn't deserve, like that I'm a brat who cries and bullies him until I get what I want.

I don't understand why anyone would keep someone like that in their life. Is it wrong to tell him that he needs to choose between staying friends with her or trying again with me?
<bot>: Ex wants to try again, but also wants to stay friends with a friend who threatened me, disrespected him and our relationship multiple times, and has a laundry list of other problems. Is it ok to tell him to cut ties?