Can I refuse to testify in court as a witness without any criminal prosecution?

I was a passenger in a marijuana related DUI offense and the person being prosecuted is not only my fiancé but the father of my unborn child (5 months pregnant). There seems to be some foul play since the people of the court is close with the DA and happens to be the ex-chief of police. His trailer was clipped by our vehicle (no damage to trailer) and my car was totaled during slick road conditions. The police officer on sight was the chief’s daughter as well and the police report has not been released for two months (not even to my insurance company) while the DA isn’t offering any plea agreements. All of this in California. We make little money. I can’t work now due to my pregnancy and they are asking me to prosecute my only life support. I was summoned and can’t get ahold of the prosecuting attorney to talk to her. Please I am in some serious need of legitimate advice.