Your questions are difficult to answer because I don’t have many details about your situation. Generally speaking, if there is no improvement in a mental health condition over a 25-year period, then it is a problem. One would expect to experience significant improvement over that period of time.
With regard to Xanax, the fact that your soon-to-be-ex uses it on an “as needed” basis suggests that he is not addicted. He may be dependent on the medication in that he knows he has access to it in an emergency situation and this provides a sense of comfort. His drinking is a concern, especially if there are occasions in which he consumes alcohol while under the influence of Xanax.
It is good that you are attending Al-Alon. You can learn a great deal from members of those groups.
You asked the question: what else can I do that I am not already doing? There may be little else that you can do. He will soon be your ex-partner. My presumption is that he will no longer be a major part of your life. That may be a desirable outcome, especially if you are no longer willing to tolerate his blaming you.
If you plan to continue having regular contact with him, then it would be advantageous to set boundaries regarding your level of interaction. For example, you could set a rule that you will not have contact with him if he is drinking. You could also make a rule that if he wants to be part of your life, then he must attend therapy in addition to seeing a psychiatrist. Your fellow Al-Alon group members might have additional suggestions for you. I wish you the best. Don’t hesitate to write again. Take care.