I was with my mom, aunt, cousins and sister nd they were talking bout some gay guys in the dance school of my sister and she mentioned one guy who says he is bisexual, then my mom said yeah sure bi people dont exist they are gay or stright and my cousin supported that idea. the thing is that she knows im bi so I ws just quiet looking at my mom and my cousin feeling a little awkward. My mom doesnt know im Bi, by the way lol
She probably just wasnt thinking properly and just wanted to agree with your mum for some reason. Talk to her about it on MSN if it bothers you that much.
There is A LOT of people that don't "believe" in bisexuality. Its pretty horrible when people say things like that, but I don't think they really understand the harm they do with what they are saying. As hard as it is, you are going to have to learn to not take it too personally. If there is a moment where it bothers you too much then you are going to have to let them know that. Don't waste your time trying to convince them otherwise; people just don't want to get it sometimes. Simply tell them to stop and to show some respect for you.
I know how you feel, I get this all the time as well. Like TheEdend said, it does do a surprising amount of harm emotionally, yet most people wouldn't even realise. As well as letting them know, try to not let it get to to you... It is the same with a million and one things in the universe - everything seems different from where you're stood, compared to another's viewpoint. If they were in your situation, they would have to come to terms with it. And as for your friend... well, it's not right, but most people tend to end up agreeing with other people's parents' viewpoints, if only to avoid an argument. Perhaps she was trying to save you embarrassment? For her to challenge it would only have brought on an argument, or a discussion at the very least. Maybe she didn't want her experience of bisexuality - being you - to come out. Arguing a point without a case isn't very easy. I hope that made sense and offered some help. I often talk a lot of crap.