I think your best bet is to treat him as someone who is ignorant and afraid.
I moved to MA a decade ago. I wasn't sure what to expect with the legalization of gay marriage. (I support gay rights, voted in favor of gay marriage, have gay friends and family, etc., just like everybody else. The only reason I thought about it was because I had young children.) Answer: not much changed. No big deal. I didn't have to explain anything to my young children- turns out the kids worked it out for themselves.
No, he's probably not afraid of gay people, exactly, but is certainly ignorant of how gay people love. Often, though, once it gets humanized, this type of fear goes away.
So I'd say, give him a chance. Think of the win if he is convinced to change his mind.
I moved to MA a decade ago. I wasn't sure what to expect with the legalization of gay marriage. (I support gay rights, voted in favor of gay marriage, have gay friends and family, etc., just like everybody else. The only reason I thought about it was because I had young children.) Answer: not much changed. No big deal. I didn't have to explain anything to my young children- turns out the kids worked it out for themselves.