Generally speaking, when an accident happens, your car insurance follows your car instead of the driver. Thus, if you let someone else drive your car and get involved in an accident, your insurance company is probably going to take the responsibility for paying the claim. That is to say, your insurance has to pay for the damage even if your friend has good car insurance coverage. The driver’s insurance policy can only be secondary coverage. When you borrow your car, you are actually also borrowing your car insurance. In most states, your car insurance is going to cover the cost of the accident if your car was at fault no matter who drives the car.
The information in this answer is general in nature and is not legal or insurance advice for your specific situation. Policy language varies carrier by carrier; your declarations page is the final word. If you're unsure, call your agent before you need to file.