does it "in a relationship" or "married" ? because there is a difference. Sometimes girls get married on Facebook and call each other things like "wifeyy" like they would say "hanging out with my wifeyy<3" or something like that. they're not really bi, they're just having fun.
im married to a girl on facebook, but im not bi or lesbian, we're just best friends and we did it for fun.. but if they put "in a relationship" with a girl then there is a possibility that they may be lesbians or bi but never jump to conclusions