How do I stop developing feelings for someone or how do I lessen the intensity?

There is no easy answer I think some one can give you, it hurts to see the quality's of a guy in someone you know you may never see after graduation I would advise you to just enjoy the time you have left as friends and cherish the memories. once you get to college and and your settle in your dorm or apartment you will make many new friends and meet guys that have the same quality's he had but you have to be open to giving them a chance you cant dwell on i wish it was "him" he was brought in your life momentarily for a reason.