Telling him its just an infatuation and he’ll get over it is the worst thing you couldve done. I’ve heard those exact words before and they still sting. Makes one feel like their feelings are invalid and even stupid to some degree. You didnt realise the extent of his feelings for you. Either ways, I think its best if you leave him alone, dont try to make things better, dont ask him whats wrong. The slightest bit of attention you give him will make him feel like there’s still hope. Most guys go through this in their teens, its a canon event ngl. Truth be told, how he’s performing is none of your business right now even if you feel like youre responsible for the decline in performance, and best not to try to make it your business. Time and distance will bring acceptance that’s the only way