How do you tell someone how you feel without hurting their feelings ?

I have a best friend who is a guy, I love him to death as a brother and would do anything for him. But the other day we were out to dinner with a bunch of friends and he drove me home. On the way home he grabs my hand and tells me he has been in love with me for so long and didn’t know how to tell me. He wants to try to start dating.

But I don’t see him like that because I don’t want to ruin our friendship. How do I tell him in the KINDNESS way that I don’t want things to change, I would rather be friends ?