If the accident caused damaged less than the deductible, then you are responsible to pay for it entirely. If it was a substantial claim on the insurance policy .. You will be required to pay the deductible, and the amount each subsequent year that suffers a rate increase. Ultimately .. YOU are responsible for any and all out of pocket expenses created by this accident... It not right that HE pay .. HE was not at fault, YOU were.
By asking you to run an errand and using his car, does not excuse your responsibility for care and control of the car.