Find out what turned him off to you, say you're sorry, and change. If that's not possible, explain to him what you perceive to be the problem, and see if he agrees. You should try to impress him or get him something. You might want to let him know that you like him.
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im having a similar problem too(; lets see here.... you could ask him, look to see if his pupils dialate when he looks at you, ask a good friend of his, do a little bit of flirting and see if he flirts back... hope that helped!
You cannot control someone else's feelings or make them like you. Focus on being your authentic self, communicate openly and honestly with him, and give him space to decide his feelings on his own. If he chooses to like you again, it should be because he genuinely wants to, not because you manipulated the situation.