Sure, absolutely. If that was a fundamental and agreed-upon condition of their partnership in marriage, then I think violating that would be as big a betrayal as adultery. Furthermore, I'd absolutely agree that a moral obligation would arise to tell their partner if they violated it.
I don't see how that affects the question I asked, though, or the larger question of the thread. I'm not arguing that fidelity is the ONLY moral obligation in a marriage, or the ONLY issue that creates a moral obligation to confess if violated. Or even the most important, necessarily.
Our marriage is fairly strongly "unfaithfulness" proof for quite a few reasons.
First, we are people slow to jump into relationships. I was never in even a dating relationship nor ever imagined having one - until her. She also never was in even a dating relationship, because her ideal man was so specific and in some ways bizarre that no man was of any interests. So emotional temptations aren't likely. Most people compromise for the best they think they can have, overlooking shortcomings or falsely filling in the blanks of what they need in a mate. We didn't. Although totally different life styles and values we lived to, neither of us so much as dated because no one was worth dating in a sense of entering into a dating relationship to either of us.
We both are people that physically would be attractive to some members of the opposite sex - her certainly moreso. But our "demeanor" and "tastes" in sexuality are not typical, so again few other people would be attractive or more attractive than each other - and on the other side of that most women would not want to be in bedroom with me or with her. A lot. It makes me laugh to think of how it would go should some man ever gain her consent and then end up in a bedroom with her. He would have totally misread her by her appearance and outward demeanor.
We also have atypical views of sexuality in the context of relationship and faithfulness. So beyond the more than usual safeguards against "unfaithfulness" far beyond most people. If the green-eyed-monster could ever be a problem in terms of damaging or preventing a relationship, it would have happened before we married. While sex certainly is a significant part of our relationship, our relationship was not built upon sex, but devoid of it.
It is not vows and promises that make for faithfulness. It is ourselves and our basic personality natures. Yes it sounds bizarre and maybe decadent, but if she truly needed other men, I'd get some great ones for her myself. Why? Because that was what she needed. Does that mean I trivialize sex in relation to her and myself? Absolutely not. Rather, she is on a far higher pedestal of importance and worth than just for sex, then even higher as the mother of our children. What our children's mother needs, if I can I'll get it for her. Whatever that might be.
Over-simplifying, our marriage is not based upon sex and we separate sex from love. Sex is sex. Marriage and love are 1000 times more important. In short, in the unlikelihood of "unfaithfulness" I am confident either of us would see it as a curious development to adjust for in the overall relationship.
Short of real and continuing real and severe abuse, we both won't break up. That is not just both our values, I know there is not one person out there that is like or could match her. And I know from reading her journal there aren't many men out there that would suit her either. In a way, it is each our very different from each other's oddness that is our stronger marriage binder and greatest wall against any challengers and comers.
People too easily get into relationships and marriage, compromise on mate-selection, too much let sex make that decision, and then too trivialize the marriage they so easily stumbled into - and too many lack morality (REAL morality) when it comes to their children. People should not bend themselves while dating to win the other person, nor overlook traits in another person figuring in the balance they don't matter if undesirable.