According to the possible interpretation of canon I find most compelling:
What comes to mind for me is Lancelot and Guinevere. According to memory, in some versions of the Arthurian legends they were deeply in love with each other, but never acted on that love because both also loved Arthur, who Guinevere was married to. This was treated as a beautiful tragedy, and both were seen as noble for never acting on their feelings, rather than not for having them in the first place. So you have two stories in parallel - the main story of King Arthur, his devoted wife Guinevere, and his loyal Knight Lancelot, but then you have a second story where Guinevere and Lancelot yearned for each other without ever acting on it because they were still loyal to Arthur. The story evolved over time, gaining new facets without changing the underlying values of duty and fealty.
Remember the story of Soizic. A woman cannot be a Knight, of course, but women secretly becoming Knights is celebrated in story and legend, even as the letter of the law decries it. The unspoken but very powerful undercurrent of Bretonnia is that people are not following the law, they are following the script. They reject the terrible world they live in, and instead play the roles of the beautiful legends they believe in. So at first law and tradition demands proper marriage and fealty, there would be many marriages where it is understood that they are playing their roles in public, and then whatever the Noble Knight gets up to with his stalwart companions, and what the Devoted Wife engages in with her coterie, is happening 'off stage' and is therefore immaterial. But then another layer builds atop that, where these unspoken roles become part of the story and then form another tradition in itself. To invent an example, a story where a marriage of convenience between a gay Knight and a lesbian Lady is celebrated because though they do not desire each other, they support each other and form a platonic bond that strengthens them both, and then the Knight kills a dragon or something. The standard telling of that story does not explicitly say that, but the writing between the lines is clear enough that almost everyone understands what it means. So it is no longer just a simple polite fiction, but it is a wink and a nudge that is worked into the story itself, and thus into society.
Like the growth of coral, Bretonnian society builds atop itself in layer after layer, resulting in a beautiful reef that can shelter its inhabitants from the brutal emptiness of the world around them.