Sharing your mental illness diagnosis is a very personal thing. Who you tell and how you tell them is completely up to you. So, do you have to tell your date you have bipolar disorder?
There are a few things to consider. The first is this horrible thing called stigma. Some people will think you are less of a person because you have a mental illness. Some people would rather not date someone with a mental illness because they don’t understand it. This does not say something about you, but rather something about them. Stigma is an ugly, ugly ignorant thing.