Why do i do this?? best friends arent supposed to be this way right?

Hey ok soooo my best friend and i met on my softball team last fall and we've been best friends ever since. We tell each other everything, even the deepest darkest secrets, and we have helped each other through our worsts and absolute lows. Although our personalitys our opposites, im shy shes outgoing. we text eachother all the time and im completely myself but when we talk face to face i act completely different. i dont understand why. please give me some advice, im really confused. i dont want our friendship to end because of my wierd behaviors. :(