I was curious, so?

howardaaron81, it is best to call your insurance agent.

http://www.carinsurance.com/CoverageDefinitions.aspx

My simplistic understanding is that collision coverage covers the car and liability coverage covers the driver.

The fact that your roommate drives your car frequntly probably means that your collision covrage would be affected. So, yes, you need (i am not an insurance pro) to "add your roommate" to your collision coverage. Your roommate also need to have his/her own liability coverage.