Why is my best friend acting like this?10 points to best answer!!!?

We've been close this whole junior year at highscool. We'e told each other alot of things includig who we like. i even told him in the past i liked him but then told him i stopped. Our friendship is really close. And well lately he's been overly flirty like smacking my *** or it when we're alone, or holding me close to him....and last night when we were talking online he asked if what he did turned me on and then jokingly asked if he could touch y .....Ok i know that is over board... but understand he is someties a little immature like that. But inside i feel eflies in my stomach everytime he touches me.IDN help? advice?