I can't get him out of my head, even though we haven't spoken for 7 months ... what should I do?

Hmm, maybe he's avoiding you because he's not sure if you're brother would be ohkay with you two dating? He might want to date you but doesn't want to risk him and your brother's friendship so he decided staying away is best. I think you should try talking to him at least one more time. Wait until he's online or go up to him in school when he's alone, or if you have his number call him.