I don't have an affair with a married guy (and I'm not planning to have one). It is probably one of the worst things that can happen. However, I don't think anybody is "planning" to have an affair. This is about feelings and sometimes things just happen. Furthermore, it always takes two. So never say never. It is hard for kids when their parents break up. However, first of all an affair must not mean the end of a marriage. Secondly, if something is wrong in that relationship (why do you have an affair?) then it does not help the kids if their parents stay together because of them.