Really? When was adultery ever defined to include anything other than a married person having relations with someone other than a legitimate spouse? [nb: the Old Testament is even more restrictive in its definition of adultery: a married woman having relations with a man not her husband; the definition is probably sex-specific because, among other things, a man's betrayal of his wife does not introduce any uncertainty about which children are biologically hers.]
It's that same fantastic section where it mention that people are living in sin, if they are not married under the same roof.
F'n barbarian asshats.