I think many of us, including you
@coz1, come at life from a Christian perspective to one degree or another. Today as in the past, Christianity is very often variously adhered to. And the Judaism of the Bible also, then and now.
The "moral perspective" is twofold. There's the Christian moral perspective and the societal moral perspective. Your characters, many or most of them, might presume to be Christians, but they aren't particularly good at being Christians. Not since King Henry, and it's debatable whether he was only differently balanced as opposed to more adherent. He did at least seem sincere.
The people of your story, just like the people in our everyday lives, tend to be relatively sincere people who also suck at being moral. We, today, have various societal moralities which vary in degrees with the Christian morality. Generally all of us probably try to uphold some degree of moral code, regardless of how perfect we are at it.
The societal perspective in King Richard's day -- and generally throughout the Western world of the time, and I'd bet within most non-Western cultures at the time -- had a taboo against infidelity because it really screws with the lineages and inheritance structure. Forgive the pun. We've seen the whole infidelity curse -- true infidelity and rumored infidelity alike -- shown in many ways in WoTR. It's the reason for all the disputes over who's the rightful king. It's the reason for the maneuvering for marriages, including Isabella's. And I would argue the characters of the story are more conscious and adherent to the idea of maintaining this societal morality than they are the Christian morality.
From a strict Christian perspective God demands/expects fidelity because sex is in His eye a symbolic thing. Yes, it's meant for procreation. It's even quite clearly meant by God to be pleasurable for both man and woman, whether a child is produced or not.
But it's also meant as a mirror of His relationship with His church. Any violation of the symbolism grieves God. It's the reason for the Jewish Law, which is very much centered around symbolism. But the whole story of the Bible -- most of it anyway -- is about how human beings (Israelites of the day, but Christians no less) really suck at being moral. Especially strictly moral. We play at it, but we suck. And God came to realize that, whereupon comes the Bible Part 2 where His plan to redeem humanity's infidelities against each other and the moral code comes into play with Jesus' sacrifice as atonement for our sins, allowing believers to be forgiven for our many infidelities.
That's where the Christian saying, "I'm not perfect, just forgiven" comes from. God doesn't expect us to be perfect any more than we can be, which we can't be. As a substitute for being perfect we are forgiven through Jesus' sacrifice as the Lamb of God.
Anyway, however much Isabella or Richard or Edmund may play at being societally moral and/or Christianly moral, they're imperfect just like the rest of us. Some human beings are better at it than others. I would suggest that the whole noble game these characters are playing makes them more vulnerable to temptation of many kinds, even as the consequences for violations become more severe.
Back to the Christian perspective... God intends for marriage to be a contract between two human beings with mutual obligations exchanged. Biblical laws on divorce, no matter how some may misinterpret them, clearly indicate there are times when divorce is warranted because the contract has been voided/violated. Our pastor made the argument that one legitimate grounds for divorce is abandonment -- where one spouse basically no longer cares to uphold the relationship and is just not there most of the time.
So I would argue that, both with his physical absence and with his infidelities, Edmund has abandoned his wife.
Again, these are all human beings, and human beings follow a human nature which is very much based in short-term pleasure and getting what one wants when one wants it. So Edmund is doing that. Isabella is doing that. Richard is doing that, though he begged off for a while.
So on one hand I'm actually happy to see that Isabella and Richard are able to find love together in a mutually supporting way. In a sense they are more closely and appropriately "married" than are Isabella and Edmund, because Edmund has abandoned her and Richard has always been there for her.
But yes, as others have said, there are some very serious consequences at stake if this relationship is discovered, and how could it not be?
@coz1 looking forward to seeing how this develops! Popcorn is at hand!
Rensslaer