I hope you have a good day tomorrow and are able to accomplish what you want. Recognize that the session tomorrow is all about you, your needs, your wants, your perceptions. It will not change things with stbx. Imagine having session with your IC and my next door neighbor to discuss your mental health and future R with my neighbor. That is about how plugged in stbx is apt to be. At best. For, his agenda is to hear something different and to get you to hear what he wants you to hear.
Stop trying to manipulate stbx or trying to have others do it for you. Stop trying to get him to see things your way. Neither of you is anywhere near an objective outlook on things. You want to think he is crazy. He wants to think you are crazy. Probably neither of you are crazy, just struggling with a major life change. Remember, it doesn't really matter what he thinks as long as business matters are taken care of. He is not your romantic partner or friend.