If you don't like him back, then remain friendly, but avoid being alone with him. With your friends around you, the situation is able to be kept on a group friendly, but not too serious footing. I don't know your ages or situation, but relationships, unwanted or wanted, are part of life and growing into adulthood.
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If a guy likes you and you don't like them back, just don't be mean, act nice. Don't act rude towards him.