It is not. You want it to be better and that includes making it cheat proof. And also keep in mind they did all of this while the spousal relationship was exactly what it was previously. There is definitely they felt the need to lie to you repeatedly and at the same time jeopardize the entire marital relationship. They bare the blame.Their whole world has been turned upside down by the thoughtlessness of their spouse.  Why then is this a pipe dream? Mainly because if the marriage was all that terrific before then they would not be going through infidelity right now.  

In some ways it is obvious what they mean. Your spouse cheated on you during those idealized times.  But surviving an affair means recognizing exactly what drove them to cheat. No question they shared many good and bad times that brought them closer together. It is like they have convinced themselves the relationship was problem free until infidelity showed up.To survive an affair means to disabuse yourself of any false notions.  To survive an affair means recognizing your spouse was unfaithful. The idea of why can't their marriage go back to what it was before. It may be hard to admit but the bottom line is there is no going back after an extramarital Plastic 2-1/2" female adapter for water supply pipe affair.

Life doesn't work that way. The second thing is you decide to stay with your spouse then you don't want the marriage to be like it used to be. That is not to say your spouse's fooling around is your fault.  Now it is understandable why they long for the past after an extramarital affair. The marital affair has hit a nerve. The relationship has changed for good and will never be the same. For example there is a dream that countless victims of cheating latch onto. This also means if you're going to rebuild the marital relationship following infidelity you will need to accept a couple of things. All things move forward.