It's good that you want to support her wants and realize that it takes time to ease the communication. Some people do that, some people don't. You should tell her how you feel, so that she'd understand somewhat what you're feeling. I know it can be hard and frustrating. Just tell her you're uncomfortable around the ex, but you don't want her to feel like she needs to lose a friend to be in a relationship with you, but there'll be times when you have crazy thinking or feelings, and you'll tell her, and work it out from there. I'm sorry if I'm not much help