Can you decide your sexuality based purely on your own thoughts?

Hi I have been constantly thinking about and trying to figure out my sexuality for the past 3 years. I have came to the conclusion that i'm bi and have even told a couple of my best friends but there is still one thing bugging me. Can I know for definite even if I haven't kissed a girl? That's the one thing in my mind that makes me doubt my thoughts and judgments ( which I do a lot!). If I had to decide without kissing a girl (which I have) I would say i'm definitely bi as the thought of kissing/going out with/being in a long term relationship with both sex's appeal to me and I have been attracted to both genders.