Their opinion is important. But at the end of the day, you have to live with your decisions, and you shouldn't be dictated by anyone else on that. It isn't just about how you might need to grieve if something happpens, but how are you going to feel about the person who 'made' you do something that you didn't want to do in regards to telling / not telling.
Just as he shouldn't be dictated to either or 'made' to tell/not tell and has to live with his decisions.

*shrug*