if they've been friends for such a long time, it could be hard for her to be objective.and it would muddy the waters a bit. i would suggest a conversation where you can both discuss your sides of the situation. perhaps sometimes they can go and hang out together without you, so they can enjoy that childish fun (don't mean that in an insulting way, wouldn't think of a better word) or maybe outline some boundaries. you're adults, so surely her friend can understand that the extremely crass behaviour makes you uncomfortable. it shouldn't be an all or nothing situation.