Find the perfect time when you guys are alone.Tell him how you feel and might even say i sort of have feelings for you. Make the time perfect so you both have the time to talk and not rush the awkward situation. Try not to make it so awkward. Keep talking and relax a little. Not a lot of boys like silent situtations, i'm pretty sure you don't either. Try to make it where no matter you will always be friends with him, even after him knowing. But remember that it won't be completely the same, so don't be too disapointed. I'm pretty sure you can do it girl. GOOD LUCK!
You just do it. But you have to come to terms with the idea that no matter what he says, you will never be best friends again. Are you willing to end your friendship in exchange for a better one or none at all?