could you maybe take him on a group ride. Maybe you telling him just isn't going to work but if he sees how the other guys ride and that you aren't just trying to get him to do what you want he will start being a bit safer? Guys are like that, some girls too. I went on one ride with my sister during our holiday and she wouldn't listen to me telling her that spinning is much better for you than mashing, she even laughed at me and told me her fiance rides like me and she doesn't understand why I would do that, it makes your heart rate go up and her cardio is her running. Riding is just for fun.