Why have I saved all the text messages from my ex? Why do I re-read them? Why can’t I delete them and delete him from my mind?

There could be several reasons why you have saved all the text messages from your ex and continue to re-read them, and why you feel unable to delete them and let go of your ex.
One possibility is that you are experiencing feelings of attachment and longing for your ex, and the messages represent a connection to that person. Re-reading the messages may give you a sense of comfort or nostalgia, or it may serve as a reminder of the positive aspects of your relationship. You may be holding onto the hope that things can go back to the way they were before, or you may be struggling to accept the end of the relationship.
Another possibility is that you are experiencing unresolved feelings of hurt, anger, or regret, and the messages serve as a way to re-experience those emotions. Going back over the messages may be a way to process your feelings and make sense of what happened in the relationship. You may be struggling to come to terms with the end of the relationship and are holding onto the messages as a way to stay connected to your ex or to try and find closure.
It’s also possible that you are experiencing a fear of letting go, and the messages represent a link to the past and a sense of security. Deleting the messages and letting go of your ex may feel like a loss of control or a step into the unknown, which can be scary and overwhelming.
If you find yourself struggling to let go of your ex and the messages, it may be helpful to seek support from a therapist or counselor. They can help you process your feelings and work through any unresolved emotions or fears that may be holding you back. Additionally, setting boundaries and limiting contact with your ex can help you move forward and start the process of letting go.