And this theory can even advocate cheating in the name of lessons is patently absurd!  I am sorry but cheating is not only cheating others but your own soul as well.  What about the cheater?  

Seems as we are so wrapped up in judgements - what is the cheater themselves thinking of themselves that they are capable of such an act?  I know when I have done things against my own better judgement I am more remorseful than when it involved being against others.  

We have inner compass points at which we learn.  We do not need such lessons from others as described by this particular theory.  This is not justifiable by such a theory or any other.  Cheating is cheating ourselves in spirit as much as others.

The theory doesn't advocate cheating..it explains why it can and does happen.  Some people need much stronger ways to learn lessons.  To feel and know them more deeply.  I'd encourage reading the book first with an open mind, then see what you think before passing such a strong judgment as patently absurd.

you already answered your question by posing this question.

who are you trying to fool?

ahhh...yourself...

Cheating is heavily defined by a large gray area.  I have several theories on why it isn't more directly approached. ( Just ask :] )
But for certain the seeds for cheating lie withing the heart, not the actions which may follow.  So if passion was the fuel, then it was cheating before the kiss.

Cheating implies for me breaking the rules of an activity or interaction.  What were or are the rules for this couple?  Have they been broken?

The question I wish to ask is - if the wife does not know then why hasn't he told her?  The reasons why he hasn't told her suggest to me that a rule or expection has been broken - ergo - cheating.

However, some replies appear to me to be focused on the moralistic and material planes.  I would rather regard what is going on from a spiritual and ethical perspective.

I also give attention to the fact that large proportion of people have extra-marital sex.  I am not condoning or excusing people for doing things which harm others or themselves.  Perhaps, only maybe, it is unrealistic to expect all people (or even the majority) to cleave to one person forsaking all others.  In which case, a vow could be regarded as an intention or hope rather than an unbreakable rule.

The connection to his wife is broken, damaged or absent and was so prior to the kissing - or he wouldn't have kissed passionately.  The kiss (or any sex) is not the breaking of the rules.  The game called marriage has been abandoned.  He is no longer playing the game or is no longer seriously committed to playing it.  The rules no longer apply, if he is not playing the game any more.  The cheat is in not telling his wife that he is no longer playing because the connection to her is weakened or absent.  Though if there is a disconnection then surely on some level she is aware of it.