I don't know how common it is, but I've had several past girlfriends express internalised homophobia against gay men, bisexuals or lesbians, and that's too damn high a number since as french leftist, I don't harmonize with conservative women. When I was younger I was naive or dumb enough to think that we would both grow as people in the relationship and some of my values would rub up on them. Now that would an instant curtain call for me, you can grow up as person in your own time, I have better things to do.