@thegreatwb
First of all, I'm sorry this happened to you if she's actually cheated on you.
You still have a chance..... Don't tell her that you know. Find a camera to record what is happening in your house while you're not there or hire a private investigator if you can afford it or having your friends do this for free, etc. First get a lawyer and find out if your state is a no fault divorce state. In certain states no matter what the reason for divorce so everything is split 50/50 including visitations rights. If you finds out it's not get proof of her infidelity and use it against her in court which will keep you from losing everything. So I suggest getting hidden cameras, get copies of her phone records, get email records, and document everything, etc......you once you have the evidence so take that information to a lawyer.
Once you tell her that you think she's cheating on you so she might be denying it since you have no proof so she will be extra careful next time and still be cheating, she will change the strategy, etc.