This is a question that a lot of good men would like to know the answer to. Especially when they are going through the experience and dealing with the emotional downfall.
It is a difficult experience for all men when their partner cheats on them. It is sad state of affairs often being left in the dark as to to why. Women have several reason why they cheat. By understanding their outlook you will be able to prevent it from happening in the future and understand better what pushed her to do something like that.
Biggest Reason
One of the biggest reasons why some women would do the unthinkable is that they just do not feel important or cherished by their men. A woman needs to feel important to her man, she needs to feel that she is appreciated and when she lacks that she might look for it somewhere else. Most women put so much into their relationships, that when they feel neglected and unappreciated, they are overcome with a feeling of sadness and worthlessness. Also know as intimidation.
Left For Another Man
First off, if your wife left you for another man, there is a chance that she was experiencing sexual dissatisfaction. While it is by no means a good reason to break years of hard work and growing together, she may feel reluctant to tell you about it and would rather seek that satisfaction from someone different providing sexual communications to accommodate her needs