I'm far less interested in the rules than in trying to learn enough to offer a useful suggestion about the meaning of the term in question. If you simply have no background to offer, you might try an abbreviations dictionary. There are many on the web.
He likens the E/B relationship to those we all (probably) remember from school. The totally-obsessed couple who for the eternity of their three-week relationship close themselves off from all of the rest of the world.
(Speaking as an observer, of course.)