It sounds like you care a lot about this guy. If you feel it is time to tell your parents, be straightforward and calm when doing so. Make sure they know he has different beliefs than what they have and show them that he has qualities that are right for you as well.
When I was trying to find someone who believes in my culture, I wanted to make sure my parents knew it was important to me. When telling them, just say how much you enjoy being around him and how much of an understanding person he is with your beliefs. It’s important your parents understand why you want to give him a chance because