Hi (((((((Soul Quake)))))) It's good to see you again. I'm sorry you're so anxious about this. I just want to say that I can totally relate to you not wanting to hang out with your boyfriend's ex. I'm the exact same way. To be honest, I also wouldn't be comfortable with my husband hanging out with his ex, regardless of whether I was there or not.
From what you say here of their behavior, it sounds like your BF's ex and her fiance are the "tools". I'm sorry it came down to this