Does your insurance cover your authorized drivers? Ensure you have liability and personal injury protection. This is in case all medical costs and damages cost more than the other driver's coverage limits.
Then, your boyfriend should keep a daily journal of pain he feels, etc, and medicines he is on and doctors he has seen. Further, if he has any visible injuries like bruises, he should take pictures. In terms of the other driver's fault, you can do a couple of things.
Either hire an attorney to represent you and your boyfriend and sue the other driver and his insurance company or if your insurance covers attorney costs, contact your insurance company to hire such an attorney.
You can sue (as indicated above) but the recovery amounts will depend on your medical costs, attorney fees, amount of damages, and if you settle out of court.