I can imagine she is getting angrier and angrier everytime she text you and you don't respond. In reality that is her ammunition. Why don't you respond? Is it because you are trying to get a reaction? Or is it because you are trying to move on?
If you are trying to move on why not just say so.
"W I know you have set up your life with someone else and that is ok I will do the same. At this time I find difficult to talk to you about things that don't have to do with the children. This of course is no reflection on you but it is more a reflection of how I feel. I think it would be healthier for both of us to maybe talk only when necessary so that we can both have an opportunity to heal. It is not only fair for you but also for me. I nope you understand."
Something along those lines
If your tired of trying to figure her out then stop. It really is a wasted energy.
