OK, well, you can still handle this.
Start sketching out your responses to the various allegations. Preparation is the key to going in non-flustered.
Also sketch out the questions you want to ask HIM on the stand. Remember that on cross-examination, you want to ask questions that can be answered "yes" or "no". It's best to ask questions like, "Isn't it true that ____ ?" Make them questions that you KNOW he has to answer a certain way, and ones that, if he doesn't answer truthfully, you can prove it. If he starts explaining or expanding on it, object to the answer as "unresponsive" (yes, you can interrupt him). The judge should tell him to answer the question.
Don't ask "why" questions or questions that will allow him room to dump on you. Any time you do a cross-examination you have two goals: First, to get him to admit things that he has to admit, that will help the case. "Isn't it true that you were arrested on ______ and charged with _____?" "Isn't it true that the house you are living in now was only provided to you as a favor by a friend? You don't have a lease or other legal agreement allowing you to remain there for a fixed period of time, do you? In fact, if your friend decides that he doesn't want you there he could order you to move out at any time, correct? And you don't have employment currently that would allow you to sign a lease, isn't that true?" Don't let him explain it, move on to the next question. The second goal is to undermine his credibility. That can mean showing bias (how he will benefit from the outcome), or prior statements he has made that are inconsistent with what he testifies to in court (be very alert to where anything he testifies to is inconsistent with the papers he just filed, for example). Keep it simple--if you score a few points, you will have done a good job of cross-examination.
You don't have to be Perry Mason. The judge won't expect you to be. But the judge WILL be looking at your demeanor, and looking for whether the person s/he sees in court appears to be this unbalanced dingbat your ex is trying to make you out to be.
Go slow, take your time, if you need a moment to find a document or think of your next question, tell the judge you need a moment.
Bully-type lawyers can feel intimidating when you are on the other side, but they don't usually impress the judge.
Hugs!!