Why does this guy suddenly hate me?

I know this guy who's really confusing. I don't really view him romantically but I don't know what's up with him. I remember a couple of years ago he was pretty cold but just this year he's become really warm and friendly. He's always made an effort to say hi to me and smile at me whenever he sees me. The way he talks to me and looks at me as well really hints at something. Like he likes me or something. that aside, the weird thing is that now he's just randomly started acting the opposite. He hasn't said hi to me for the past week, he avoids eye contact and he hasn't smiled at me. I've done nothing wrong so why is he suddenly acting like this?

Why does this guy suddenly hate me?
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