Wow--the comment about wanting to live full-time with mom would be a punch to the gut, for me as well. Does she know you read your texts? I wonder if, after you expressed your frustration at her, it was simply a safe way for her (unequal in power dynamics) to respond by expressing her frustration at you.
At 10, the decision isn't something she controls. You have years to improve your relationship before she's at any point where she could make a choice, and hopefully, you and your XW continue to get along such that neither of you undermines each other on this journey of learning to be good single parents.
