Why should she change her relationship with her ex just to help coddle your insecurity? She has a good relationship with her ex husband, which is great for everyone involved, especially their children. So few ex partners have a positive relationship, so it should be looked at as a good thing. You have been together for long enough that this shouldn't be a continued source of anxiety for you. You know this woman. You love her, and she loves you. Has she ever given you any reason to believe she would disrespect you and your relationship by acting inappropriately with her ex? I'd love to know why it bothers you that they have a friendship. I understand that it can be tricky to stay friends with someone you were romantically linked to, but they have children together, and they were married, so it's another level of relationship that they have together. I don't think that you are wrong for feeling the way you do about it, but I do think you need to drop it and decide to trust her. She has been clear that she has no intention of changing her relationship with him, so you have to respect that.
"Caring is not an advantage."