Ask him to participate in a little experiment. Place your hands on either side of his head, betwean the ears and the eyes, and look into his eyes.
What ever you feel when you look into his eyes, go with it. When doubting your emotions for someone, look into their eyes!
Obviously he will think this is rather strange, but don't you worry, you won't have to explain. Either because you don't care about him and him thinking you are strange matters little. Or because you will distract him by asking him out.
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Once I knew everything, then I got smarter, now the only thing I know is that I know nothing.
Strange how that worked out isn't it?