What exactly can be causing my boyfriend's ear and jaw pain?

See a dentist: Ear and jaw pain need to be evaluated by a dentist to determine a diagnosis, then proper treatment to resolve the pain. It could be a muscle issue or there could be an infection in the area. Call a dentist asap.

A few things: Hard to say from information provided. If it is a first time thing, could be an infected wisdom or other tooth. If recurrent, accompanied by joint noises and restriction of opening, could be TMJ. See an oral surgeon, if negative for teeth, ask for a referral to a TMJ expert.