How do you make it clear to a guy you're not interested anymore?

You need to tell him that you don't feel that way and that you will never be more than friends. If he can't handle that, it is best you do not see each other. As long as you hang out with him without saying anything and letting him think there is a chance, he will never give up his feelings. If he can't let go of his feelings for you, he will not be able to watch you just move on or be friends. Tell him how you feel and that you guys shouldn't be around each other.