Why does he still treat me like this?

It sounds as though he outgrew the relationship/lost interest in it or you/developed feelings for someone else. Why he treats you harshly, only he can answer that. Like the person above said, there's no point trying to understand it. He's obviously not interested anymore and wants to move on - he will continue to act this way until you leave him alone. Sometimes people use the ''I still want to keep you as a friend'' line to ease the pain of breaking up.