You can casually talk to him and say that according to all Ayurvedic books you have read, self-gratification is unhealthy and as per Ayurveda, refraining for sex and self-gratification increases Ojas. And then if he says that he agrees, then you can question him about the massage. SO asking in an indirect way or to create an impression that you are not comfortable with the current situation might help in this case. It might make it easier for you to broach the subject in a passive voice. If he is intelligent then a mere hint should suffice to let him know that his methods are not appreciated.