At this point you can either sit and wonder until she finally walks out on you and leaves you for good or you can start now to figure out your part in the debacle. Because as sure as night follows day, no matter how morally wrong she is, there is blame for you in this situation as well.
"Why would she even cheat on me?" Is a classic question that gets asked time and time again and not having the answer to that question can drive you crazy! Here's some pointers...
Why She Will Cheat On You!
Attention - You give her everything money can buy, but she cheats on you. Everything money can buy is great for some women, but have you given her your attention?
Most women need to feel validated and wanted and that means you have to make time in your life to show her that she is important enough to make time for. If you are consistently too busy, or too stressed, or too tired to spend some quality time with her, she will begin to feel marginalized and she will go looking for the attention that she needs from someone else.
Lack Of Intimacy - Don't fall into the trap of thinking that women don't enjoy or need regular sex. Many women are just as sexually expressive as many men and if your love life has died or become boring and static, then some women will go outside the marriage/relationship to look for the excitement that they need.
If you need to spice things up, then do so now before she even gets the thought in her head that things aren't quite right.
Lack Of Communication - Over time it can be difficult to maintain healthy and regular communication. You both get busy with careers or children and life in general and before you know it, you haven't had a chat in days/weeks. If this is the situation then you really need to stop and make time to find out what is going on in her life. How she's feeling about the things that are important to her.
Romance - Again, time can rob you of romance but if you want to stop her cheating on you, you absolutely better make sure that you make time for romance.
Women need to feel as though their man thinks they're special. If you've let yourself go and are regularly found slobbing about in dirty sweats and sneakers, then you need to get yourself in shape and treat yourself to some new clothes. Once a month take her out and make a fuss of her. Get a regular "date night" going on! Help out around the house! All of which will boost the level of romance in your marriage/relationship and help to stop her cheating.
Basically the top methods to stop her cheating are really to do with making time for her and having an interest in what she does and what she wants.
All that said, this is not to blame you for any mistakes you might have made, it is simply to steer you on the right track now!
So concentrate your efforts on these basics and you won't be sitting in a room wondering why she would ever cheat on you.