Each and every person gets there in their own way, sometimes it takes a while... sometimes it never happens. All you can do to help them is lay it on the table for them. You can lead a horse to water but you can't make it drink!!
My whole family poke fun at me for being interested in parasites and how they infest people. They think its just a phobia... little do they know its a fact of life!
You're not alone in this! Maybe if you can give him EVIDENCE, he might believe you.