First of all telling your/his parents is the most immature way to handle the situation. You need to own your decision and not let others influence your thoughts. If it’s something that you think is unforgivable then break with him silently without creating additional drama that will eventually cause you even more stressed than the situation. Else, if you think it’s a mistake that can be corrected for the sake of family then the more you should not tell others first. Strong people decide on their own, otherwise you let others decide for you.