Historically, infidelity has always been basis to end a marriage or relationship. From what you wrote, this is the second time this has happened. So you should not let yourself be guilted to stay since her promises to change are at high risk to fail again sometime in the future. You have the right to forgive and stay, as well as an equal right to say "enough, no more". Your choice. She can't make you stay in the marriage just as you can't make her stay. And the domestic courts are not there to mend marriages, they deal with people as they are, they're structured to unwind the legal issues of the relationship — custody and parenting first, then possible support, then finances regarding assets and debts.
Frankly, unless she gets an experienced and perceptive therapist, gets effective therapy and applies it diligently in her life going forward, then she won't improve. If she doesn't get past the Denial, Blaming and Blame Shifting, and work hard to overcome her sabotaging tendencies and skewed perceptions, then the past will be a good predictor of the future. More than ever, actions and follow through mean far more than words and promises.
- Is she a controlling spouse, demanding compliance or else?
(Then you may have a real struggle on your hands, it's hard to break that desperation to dictate and control.) - Has she threatened to make allegations of DV or child abuse?
(If it has been contemplated or threatened then it will happen, given enough time.) - What concerns her most — her connection to her child or her adult relationships/affairs?
(This is an indicator how bad the conflict may be.)
In many cases here, mediation early in the separation or divorce is not successful, the sense of entitlement is just too strong. If it works, great, but don't depend on it. Settlements are more likely to occur just before major hearing or a trial, often several months or a year or more down the road. My settlement was near the end of my 2 year divorce, just minutes before our full-day trial was to begin. Besides her predictable relentless obstruction, she wanted delays because the temp order was all in her favor.