Why is he ignoring me?

So we was talking for a while he was the one who approached to me he would always say hi and then he would even come when I would tell him to come to me a whole month he started acted distant and telling me what do you want now he tells me he don’t want me anymore when we never been together he is my coworker every time we see each other at work we ignore each other
Why is he ignoring me?
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