What state do you live in? Have they given you a witness advocate or a woman's representative (every state calls this something different but it is a person that will stay with you throughout the proceedings, explain what is happening, answer your questions and support you). If not, who is calling you and talking to you? And have you been hoenst with this person about the past abusive relationship and your fears? Do you know what they hope to achieve by sending him to jail (he obviously can't pay from there) and do you know for how long he will go?
Generally, when it comes down to it, depending on your state, you probably are not an integral part of this. He was ordered to pay support, he did not, he owes, and they have to decide how to deal with it. They may want you to testify about when he stopped paying and that sort of thing, but depending on your state, they might not even need you for that part adn can use other sources for that evidence. The onus is on him to prove that he paid (which doesn't even seem like an issue that he is attempting to fight).
In my state, the judge will not see you in chambers, but he/she will do everything possible to make you comfortable. If I remember correctly, you said that your ex is already in custody, right? In that case, he will be transported to Court from jail and will be in the dock in the court and usually that is far away from the victim. Has he threatened you? Is there a restraining order in effect right now?
Also, don't be afraid to call a lawyer in your area to discuss this. A talk to people all of the time on the phone (without charging) and provide a little guidance on their situations. As long as you target your questions and don't take a long time on the phone, I think that a lot of people would take five minutes to assist. Plus, you will get guidance here too. I say this b/c some states have ramifications for the party that doesn't show up. In my state, in CERTAIN CIRCUMSTANCES, when the victim doesn't show, the Court may issue a warrant to allow the police to go and get her and bring her to Court to testify. I am not trying to scare you but you want to make sure that you know what you are up against and that you do the right thing for you.
When is the hearing?
Christine