The most important thing you should do or should I say shouldn't do is accuse her without having concrete proof that she is cheating. You have a couple of choices do some investigating of your own or talk to your wife and ask her if she is seeing someone else. It would be better for you to communicate with your wife. if you have to invest your wife and then you find out that she didn't cheat then the marriage may be strained because you didn't trust her so this is a touchy subject and that is why you should make sure you have proof.
If she wants to save her marriage also it may be helpful to consider Marriage counseling if that is something your would consider.It's going to take time and proof that you can trust her again and if she isn't willing to do that then the marriage may be in trouble but if she wants her marriage back on track she is going to have to start being honest with you about her whereabout and what she is doing while she is out and about. What you are going to have to do is make sure if you decide to give her another chance that you can forgive what she has done and work toward getting the trust back but don't do that if she hasn't prove to you that she is worth another chance. I think Marriage Counseling would benefit you both the most, for you to teach you coping mechanicisms and for her to figure out why she stepped out on the marriage in the first place.