'Tis a good article. the only bit I'd take issue with is:-
"Where three people are each faithful to the other two, that could be called a polyfidelitous triangle."

I don't like the use of 'faithful' in this context and would prefer something like 'have an exclusive relationship with'. Use of the word faithful implies that other ways of doing things are unfaithful, whereas I regard faithfulness as being about keeping promises.