I'm gonna do it

Okay so I'm gonna tell my best friend that I have feelings for him. I'm terrified cuz if he doesn't feel the same way I don't want him to treat me or our friendship differently or if we try a relationship and it doesn't work out I don't want to lose our friendship. I'm never afraid when someone decides to walk out of my life because I'm not the type of person that's gonna beg someone to be there but him I don't think I could handle that. What do I do?