I think I have a crush on my best friend
That's interesting. What makes you think you have this crush?
A strong and endless chemistry, my heart is beating fast when I see them and he has a cute smile and intriguing eyes.
This might make your friendship harder for both of you. You should keep it to yourself unless you think they feel the same way.
But I really want to tell him how I feel.
It's very risky admitting you have romantic feelings for someone that you're good friends with. If he doesn't feel the same, then the friendship might dissolve. I think you should wait a little while to see if you think he feels like you do.