I understand your fear, but I think it is misplaced. Your boyfriend is entitled to choose to be with whomever he wants, as are you. He has chosen you, and you are both happy with that situation. If his parents have a problem with that, they are the cause of the trouble, not you. You cannot hold yourself responsible for their reaction.
The situation could get ugly, no lie, and perhaps you want to consider whether or not you want to be in the room at the time. That is fair. But it is not a reason to leave him. Any grief he gets from them is an indication of how much he is willing to put up with to defend you. That is the kind of man you want to stay with: someone who will stick up for you.
It doesn't sound to me, based on how you describe him and his approach to talking to his parents, that he is the type to cave in to pressure and reject you on their insistence. But, if that is what happens, that is the time to reconsider the relationship, not before.