You as the driver are ultimately responsible for actions behind the wheel of the car and thus if you caused an accident to occur then you can be held personally responsible for the damages you caused to another as well as the car you were driving.
It would appear that your friend's liability insurance is taking care of the damage to the other vehicle involved however your friend does not have physical damage coverages to cover his or her own vehicle. Without collision coverage to make a claim for the damages to the car you were driving then you as the one responsible for the accident normally can be held liable.
When you borrow a car or other property from someone there is an unspoken agreement that you will return it in the same condition as when you took the property. If you cause damage to the borrowed car then your friend can request you to pay for the repairs. If you choose not to pay or cannot agree on the cost of repairs then the car owner may take you to court and provide the court proof how much it will cost to fix the car and request a judgment in that amount.
Also if you borrowed a friend's car then as a good friend you will normally want to make sure you fixed any damages you caused so that you do not put your friendship at risk over a minor accident in which you were at fault for. We have seen friendships broken apart over a few hundred of dollars. It is unfortunate that car repairs cost so much but when you caused the damages you should assume that responsibility and get the car repaired back to the condition it was in when you borrowed it.