how do i tell him?

I like this guy. Which normally would be okay if he weren't my best friends brother. He is also my friend. i know that he has feelings for me and he knows that i have feelings for him but we are both scared to tell each other. I want to tell him so bad because i see him every day. i cant stop thinking about him. how do i tell him. What am i supposed to say or how am i supposed to react? I have no clue. any ideas?