Break ups

so I really want to break up with my boyfriend of 7 months, although I'm not sure how to go about it. I'm only 15 so its not like I can drive. We are both on summer vacation, so I think the best way to do it would be over the phone. He is really a sweet guy and I don't want to hurt him. I love him, but its more of a brother/sister love. I just feel like we are growing apart. I don't even feel like a couple when I'm with him anymore. It's just hard because we have been together for so long. Have any advice on how i should go about this?