Awe that is just so freaky adorable! He will really really happy when she can't be just his friend anymore. Honestly I think that might make him unable to speak. Or he will end up saying something cheesy like. "I've never seen you as [b]just[/b] a normal friend, Billie."

I don't really see a problem with the group knowing either. Not even Clary knowing either. Just she would have to keep it from everyone outside of the group.