This can be tricky. Since he doesn't live in your residence full-time, he no longer needs to be listed on the policy. But, his ability to use your car will depend on the specific conditions of your car insurance policy. Namely, do you have what's called permissive user. Permissive use or user refers to someone who can drive your car with your permission. The stipulations for this are the individual cannot live in the address listed on the policy, use the vehicle more than 12 times a policy period, or be an excluded driver. So, to sum up, I would confirm the following:
- See if your policy has a permissive user clause
- Confirm the number of times an unlisted driver can use the vehicle
- Confirm your son is not an excluded driver
This should help alleviate any confusion you have regarding whether or not your son can borrow the vehicle without needing to be added to the policy. If, however, you do need to add your son to the policy, you can add and remove him for the time needs to use the vehicle.