Sorry you're here, but now that you are, realize you are among friends. It may get a little tough around here, but we are all here to help each other through some VERY difficult times.
In terms of your specific situation (sitch from here on out) I am a little leery of giving advice because I think, and please, someone correct me if I am off base, when you are dealing with a "serial" cheater, someone who has multiple affairs, it can be evidence of something more, or at least different than the standard "bad (and bad is subjective) marriage, escape affair", "One night stand", or "Fell in love, didn't mean to" syndromes we see here a lot. If she is doing this all the time, with 3 men that you know of (sorry to say there may be more) then there may be deeper issues here. Does she have any history of abuse as a child? I am just looking for something that may clue us into why she would adopt this behavior.
She said she's done cheating, right? Is she willing to be "transparent" to you in terms of cell phone bills, email, etc? Has SHE said why she cheated? Does it ring true to you or is she making excuses?
As for you, as per the "books" we talk about, that this site was founded on, Divorce Busting and Divorce Remedy, you need to start to look inward. You need to really start the process of learning how to do for yourself in terms of happiness and direction. Since you've been through D before, I know you don't want to do it again, but the first step to that is to realize you can't control your W. You will have to work through this process. It starts with you.
I feel for you. It sounds like you were doing the right thing, but the last thing you need to do is to start looking at your marriage, as I think you already have, and discover what needs to change if and when your W is "back". I think in your case, as I said above, that may not be enough. She will also have to figure out what this habit of cheating is all about and probably get some counseling. Maybe marriage counseling would be good for you both, but first, I think she should go to IC.
