Help please?

I was driving a car I borrowed by my daughters father he used to have medium coverage I thought he had that covers other drivers. I borrowed because my car I had just bought had to go to a shop for a 6 grand fix I can’t even afford. I rear ended a car barley he breaked right when everyone was turning right. His insurance doesn’t cover me. Now what do I do? I don’t have his info or anything or what will happen and my ex just gave me the paper that was given a month ago? Help this is his car