The inflamed tip of the penis (balanitis) could be due to infection, irritation or allergy. Infection is less possible because you, as his female sexual partner, would experience the same infection in or on the vagina and the infection would be present all the time not only after sex. Physical irritation is possible if there is not enough lubrication during intercourse. An allergy caused by a lubricant is also possible. Your boyfriend should see his primary health provider and a dermatovenerologist if necessary.