Alot of talk about cheating yet, we don't stop and think about the aspect of "why" some cheat? It's not as black and white as some would have it, or some would like it to be.
People cheat for many reasons but, being neglected, or being taken advantage of is one of the biggest reasons according to statisics. IF, you have children, lets say, and you are in a marriage such as this, many people feel the need to stay together for the children's sake and don't want to mess up the family until they have grown up.
If either one of you is taking the other for granted, and ignoring their spouse, sooner or later, this is going to cross your mind. Everyone wants to be loved, and treated with the same respect so, when that stops, so does the communication, and the love.
So, What IF he/she never paid you any attention, and nomatter what you did, or said, that didn't change..
AND, divorce didn't seem to be an option? What would you do??