I know this is kind of old, but have you all seen this?
Basically the NYT Vows section featured the wedding of a couple that met and fell in love while they were both married to and had kids with other people. They say there was no physical affair before the told thei respective spouses.
http://www.nytimes.com/2010/12/19/fashion/weddings/19vows.html?_r=1&adxnnl=1&ref=weddings&adxnnlx=1292955898-Kop4dwlujCwPG45xwO6t3w