If an ex publish damaging material about you on social media, you can respond accordingly. As though what was going to be appropriate or best will depend on the particular circumstances at hand. Was what they publish true? Was it not true? What is the specific allegation or misconduct charge or charges that you're facing from the school? Those would have to be responded to accordingly. Necessary defense would have to have to be prepared and presented at the given time.
Conduct charges can potentially be pursued against your ex for doing so. Outside the school setting, a civil action such as a defamation suit can be filed against your ex, if somebody was looking to go that route. There are different options. Of course, if you're facing misconduct charges, that is a serious situation, you need to respond accordingly. You need to take the necessary precautions before you engage with the school. Having an experienced attorney adviser will be your best ally in doing so, will help you best understand and navigate the process.