What do you do if someone doesn't believe you like them?

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I have been talking to a guy for more than a year and we have become good friends. We often fool around and flirt but everytime I tell him I like him he says it's not true. He doesn't believe me, and is constantly saying why do I like him if he's not cute. I told him many times that I don't like him physically, I like him because of the way he is. He still doesn't believe me. So I was wondering, what would you guys do if someone doesn't believe you like them?