Why do I have to constantly prove to people im Bi?

Being Bisexual, even in the LGBTQ+ community, is often seen as "not picking a side" or "being confused" and often people do not believe it because they do not understand the fluidity in their own sexuality. This being said you should never feel like you have to prove anything to anyone regarding your sexuality or orientation.

People who only experience attraction to one gender can find it a little hard to understand that some people like more than one gender. There's also the misconception that bisexuality is a phase due to people experimenting with their sexuality usually adopting the bisexual label. Sometimes the label fits, sometimes they end up going back to the straight label or going to the gay label. For those who don't understand how someone could like more than one gender, they may believe it's made up because it doesn't fit their frame of logic. There are a lot of misconceptions around being bisexual, so sadly many have to constantly prove themselves about it.

You dont. You are free to be whoever you want to be and you dont have to prove anything to anyone other than yourself.