Related to the
midlife crisis, the truly adulterous fling (which requires actual
adultery, as can only occur when one or both members of the
couple are still married to other people) falls into three generic categories.
1) The fling may be an attempt (usually by the male) to stave off what he suddenly perceives to be the advance of mortality. While not every philanderer admits this to himself, the male may be trying to have a second life. This category is characterised by overt, almost excruciating honesty. The male will always tell his wife about the affair, since it isn't really about dumping her, but is more about expanding the circle. He will also expect to have more children with the new love interest, and sees the opportunity to procreate again as an historically important experiment. He is in love and makes all the usual mistakes. (see polyamory and polygamy, interesting experiments which largely fail to create happiness. The partner (usually female) in this mode, if unmarried herself, is usually younger and half expects the affair to end badly. She may have low self esteem or conversely may be slumming, a girl on top, just be fooling around, trying to get knocked up, or head over heels in love.
The male and female generally find their opposite number to be beyond belief beautiful. They gotta have it and make love six times a day for hours at a time. They literally dream about each other and exist in the mindspace or meme of shared love.
This type of fling lasts years, unless it ends in a crime passionel
2) The fling is about revenge. This mode may occur if a spouse (or partner in a mode 1 AF, above) casually disses their partner by engaging in a mode 3 fling (below), or, more seriously, either takes a lover or leaves town. Walkabouts are becoming surprisingly common. In any case, a mode 2 AF always ends when the active participants realize that they are merely trying to re-create the Lost Other which will never work. The mode 2 AF can lead back to the original marriage, to church, to rack and ruin, often through drink and the devil, or rarely, to finding oneself. Much unfortunate social detritus and crapola is often scattered like so many verses in a bad song sung by Barry Manilow or Barbra Streisand. Of course, great songs sung by Patsy Cline also cross this territory.
3) The parties were drunk. It was lust and the swirlies. Your wife or husband will not believe this or forgive you, but it didn't mean anything and should be forgotten and not repeated.