He thinks I’m mad at him and is distant?

A guy who I have been told is interested in me thinks I am mad at him. I’ve told him multiple times that I am not and his response is that “I know you hate me”. It’s over something so small, I wouldn’t be mad at him, but he won’t believe me. My friends have also told him that I’m not mad at him. He still talks to me, flirts a little less, but is overall distant. Why would he be acting this way and also not believe me?
He thinks I’m mad at him and is distant?
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