What can I do?

If this boy has no interest in you, you should look for someone else. I know that it hurts you, but if he doesn't want you, there is nothing to be done. You will have to live with the pain until it goes away. Try to spend as much time as you can with your friends, and try not to think about him all the time. Such things just require a lot of time, and you will have to live with it until you stop hurting.