To the poster of this thread: I think most of the advice people have given you is wrong. You shouldn't tell him that he's deluding himself, and you shouldn't pretend nothing happened.

TELL HIM THAT YOU LOVE HIM and that you'll do stuff with him to a certain extent.

You're siblings, and siblings can and should love each other. Anything short of making out is absolutely fine and you shouldn't feel pressured by his "romantic love". You can go out on dates, hug, snuggle, sleep in the same bed. As long as you're comfortable with it you can take comfort in the fact that he loves you too.

He already got the message that you can't return his feelings. It was awkward, and that's too bad. But that doesn't mean you should pretend you are just in a distant relationship. Take this as an opportunity to become closer. Don't just pass it up. That's horrible.