My girlfriend entertained the idea of becoming friends with one of her previous fuckbuddies. It's a guy she was fucking prior to me, ending it when I told her I wasn't gonna keep seeing her if she kept fucking him. She obliged. He got mad at her and didn't talk to her for a while.

Yesterday she told me she was gonna cultivate a friendship with him.

I told her I wasn't comfortable with this, to which she replied "don't make me choose". I told her to choose. She became silent, refusing to give me an answer.

How do I handle this?

Do I even give her a chance at stopping this, or is it a simple break up? (Soft/ hard next are the terms used?)