Looking for info to disprove this stigma, I don't really have much other than one academic research paper I found but I don't think if the guy I'm arguing with would be willing to sit through and read that. He dismissed it as queer theory which he says has been "debunked" idk what the hell queer theory is. Anyway from what I can tell with this dude the simple and more obvious the better but it must also be backed by peer reviewed research
Then I'm sorry for your loss, genuinely. You have to consider, even being friends, if he cares about your opinion at all or if he just sees you as a lib captive audience to troll. Ultimately it's not your responsibility to fix him and you shouldn't feel bad if you can't.