I have done a great deal of reading on the topic of infidelity/affairs and how destructive they are. I have also spent a lot of time both here and at marriagebuilders.com(MB) and have noticed some very different approaches to this topic (I hope we can discuss the relative merits or each without defensiveness or rancor).
DB seems to treat an affair(A) as almost incidental and not the root cause of a WAS or impending D. DB recommends NOT snooping to find out and NOT exposing the A if one is known and ongoing. DB seems to focus on "competing" with and outlasting the A rather than threatening its existence.
MB pretty much assumes that an A is the primary reason why one spouse is talking/doing separation and/or divorce. MB unequivacably states that, no matter what problems existed in the M before, the A must end FIRST and problems in a M cannot be resolved/negotiated if there is a 3rd party in the picture. MB strongly advises that an A is very likely going on even if the LBS doesn't know it, information must be obtained, and the A MUST be exposed ASAP.
From my own personal experience as well much observation and learning, I would argue that infidelity is VERY OFTEN present when a M is in severe crisis. The wayward spouse will lie, deny, scapegoat, and rationalize like crazy. I have learned to recognize that the vast majority of divorces are sought and entered into because one spouse is straying and has become convinced that the M isn't "right" and the A "is" (not because of the lame excuses of "it didn't work out" and "we are incompatible"). Simply put, if a WAH wants a S/D, he is very likely cheating and if a WAW wants the same, she is almost always cheating as well. [Domestic abuse shelters are full of women who refuse to leave their unworthy husbands--it is exceedingly uncommon for a wife to abandon her marriage/home/family UNLESS/UNTIL there is another man in the picture to run to...simple fact.]
