
You are totally mixing things.
I will talk about real life and not the manga because it is what you did.
Have you ever wondered why dating comes before Marriage? Oh. Yes, because it is when you are going to make sure that this special person will give you happiness, is going to be by your side in good and bad , and will only love you (if it's not an open relationship).
So when people are completely sure of these and more aspects they get married.
Actually not only married couples should talk, Evey couple should do it regardless of their "legal and moral commitment". Why? Because there are a lot of situations that can be avoided by talking and there are situations when it's solution just require a simple talk between the parts involved.
Honestly this is all very idealistic but this is how it is suppose to happen.
And cheating is a big no! It doesn't matter if it happened just once, because you trusted that person and when they cheat you end up losing confidence not only in that person but also in yourself.
Not I don't see how your comment is related to the manga because they aren't going to divorce, they're just fighting and most probably figuring out things.

As a mature independent woman, if my husband cheated on me even once, i am outta the relationship. Really, i am not that generous with my 'chances'. Some will talk it over and pretend that it never happened, but for me who have a darn strong memory wont be able to take any type of infidelity. If i gave my whole life to someone, i want him to do the same. If he is not as committed as i am, get out.

This is somewhat cultural, but I am on the same page with everyone else here... If my husband doesn't have enough respect and love for me to help his dick in his pants, I am gone.
If my feelings mean so little to him that he would sleep with someone else, then the relationship is already over.
People don't change. He'll do it again. Maybe in 5 years... Maybe in 20... Better to get out right away.

Opinions are great, we can all agree or disagree for whatever reason. I'm not out to change anyone's mind. Commitment means different things to different people, for some it means giving a person or relationship a chance, working at making it better before walking away. Sex friends, boy/girlfriends, lovers are only practice for the real thing. It is something you'll have to talk to your partner about and make sure you are aware of each other's expectations. Before I got married we had heated discussions directed by the premarital counselor on this and a crapload of other stuff.

Personally I don’t care if people divorce or slowly work things out and seek a compromise (or some form or repentance). My solution is pretty easy: don’t get married. No marriage, no divorce. Better yet, unmarried couples can work out their problems and don’t need to think about divorce! It’s easier to break up too (if that’s what it comes down to). Also, this route is more cost-efficient. No need to pay thousands for a wedding ceremony and then another fee for the divorce...
Yep. Best to not get married. Besides, common law is a thing now and it’s basically marriage without actually getting married.
In real life, mature minded married couples talk about their problems and do NOT immediately divorce after a single infidelity, they forgive each other and try to improve the relationship...both sides work on their accountability to each other and to the relationship. It Is NOT like dating where there is no legal and moral commitment and you can just break up over whatever.