Well, you've eased the pressure a little bit by telling us. I would give it some time before making a decision. If you like him in that way, can you ever really be just friends or are you destined to keep torturing yourself? I'm sure you have many fine qualities that another guy would find attractive, maybe adjust your focus to someone who will return your attention.
I like this boy and I've known him forever but he likes this other girl. She's pretty, athletic, funny, and smart and just his type. But here I am. I don't know if I tell him and ruin the friendship or just keep it bottled up?
Since he likes another girl, you shouldn't come in between them. That is not right. If he quits liking her, then think about telling him you like him.