You said you're close to this driver so maybe they give you a great deal. Most drivers charge per person. Just so you know the going rate with a deal for airport transfer in a private ride from MBJ to Negril is $35-40USD/person and that's on low end because many quote more than that nowadays. Inflation hasn't skipped Jamaica. You know your driver best so pay what you're comfortable with but $35-40/person is what most would expect these days.
Yes he is a good friend that I have used for years. I have about 3 drivers in my rotation and none of them charge per person but I am aware that most drivers do. I'm not the typical tourist looking for the cheapest Red Stripe so I always want to be fair with my pricing.