Quite a few reputable studies have shown that sexuality falls along a spectrum. In other words, most people are neither completely heterosexual nor homosexual in their emotional, sexual and social preferences over their lifetimes. Some may fall near either end of the spectrum. Some fall toward the middle of the spectrum. Some fall between each pole and the middle. There are as many points on the spectrum as there are people.

Yet, as you point out, there is a common belief that bisexuals are just straight people going through a phase or just gay people who have not yet accepted themselves. While some people do go through a questioning period and eventually end up realizing that they are either gay or straight, many who consider themselves bi find they have the potential to be attracted to both men and women throughout their lifetimes.

Other misconceptions are that bisexuals will sleep with "anything that moves" and that bisexuals must have both a man and a woman to be satisfied. However, the range of bisexual behavior is as wide as the rest of the population. Most bisexual people have one girlfriend or boyfriend at a time, just like the majority of the population. A small percentage question the notion of monogamy and have multiple relationships by choice--but some straight and gay folks do this too.

You can try to explain what you have read here or you can refer your mother and friends to the many studies you can reference online (including studies by Alfred Kinsey and Fritz Klein) but there is no guarantee that you will convince them of anything.

Perhaps the best thing you can do is be yourself and try to find ways to be more secure with who you are. You will probably meet other bisexuals who are secure in their sexuality and who have known that they were bisexual for a good long time. You will likely begin to feel more confident in your own sexuality, whether it shifts or stays the same, and what others say about bisexuals may not bother you as much.

Take care.