I unfortunately had something similar growing up. Weird thing is, I even knew a few bi/gay people growing up (not directly friends, but friendly), and I didn't have any issues with them. I just didn't associate them with what I had in my mind as "gay people." Those people were different.

Wasn't until a dude in our department on the ship got Honorably dishcharged, and I found out it was because it was discovered he was gay (before gay people were openly allowed in the military; Don't Ask Don't Tell was in effect). I realized that I didn't see him as "off" in any way when I didn't know he was gay, and there really wasn't anything that felt "off" after the fact. Dude was one of the hardest workers we had, just happened to be attracted to other guys (actually had a very steady non-military boyfriend, found out).

Shit changed my perspective on a lot, as I started reevaluating a lot of past misconceptions I had growing up. It's part of the reason I'm sort of sad that shame culture is so big right now. I think some of those people with fucked up misconceptions about others might be able to be persuaded, but not if they're always being thrown on the defensive.