I will not trouble you with the insanely complicated context of this legend and how we came to know about it, suffice it to say that this is a 12th century legend or, more accurately, literary tradition from Silesia, now Poland, which reports how Vladislav the Exile got his moniker: he was exiled by his younger brothers, allegedly for blinging an influential magnate, Peter Vlostovic. There are multiple fascinating aspects to the story, such as how it was used in the past and how it survived for us to access today, but I will keep it short and jump right in just to bring to your attention a single detail that I think is quite telling: the parallel between fidelity to marital and governmental vows. 

So here is the story: Vladislav the young prince and the magnate Peter, an older adviser of the old prince who had divided the kingdom between his sons, go hunting and go into the forest so deep they can't get back that day, so they camp for the night. At the campfire they are eating their supplies and sucking on balls of snow, so to cheer things up the prince says: 'look at this great feast you are having with your sovereign! I'm sure your wife is at the moment better entertained with your abbot.' Interestingly, at this moment the narrative tells us Peter did not take this well, but still he jokingly replies: 'Just as yours with that German knight!' After they return home the prince is withdrawn and his wife Agnes (who is German herself) wants to know what's wrong with Vladislav, so she eventually cracks him open and he tells her about the conversation in the woods. Agnes (who is the antagonist in the work) convinces him he has nothing to worry about but begins to hate Peter who said such things about her. She plans to get Peter killed, so she convinces her husband of a plot by his younger brothers to depose him and tells he he should be more aggressive and take from them their provinces, 'since if they illegally seek what does not rightfully belong to them, let them also loose what is rightfully theirs.' The nobles of the land attempt to intervene, because in the story the younger brothers of course are innocent and no one wants a civil war, but Agnes convinces Vlad not to hear them out. Peter then attempts to intervene as the nobles' spokesman, but after he speaks of peace, again Agnes convinces Vlad that he should be tough and that Peter is a traitor.

The story goes on, but that's all we need to look at infidelity. The marital vow is a contractual obligation, but so is rule. In a marriage the parties have exclusive rights over each other's bodies and should hear each other out while in a kingdom the ruler cannot be touched and has rights over the bodies of his knights as he can send them to battle, in exchange the knights have a right to counsel the ruler. Both contracts create a corporation, an entity made out of units. So the main tension of this part of the text is the conflict between the loyalty that a husband has to his wife and a ruler has to his people. Each time the prince neglects his duty to listen to his subjects he is immediately shown to listen to his wife. The author does not propose that the contract between ruler and ruled is more important than the one between husband and wife, but we are told that Agnes is indeed an adulteress, implying that since she went against the marital contract, Vladislav should stop listening to her. What I thought would interest you here is the conscious treatment of loyalty in a marriage with loyalty in politics, perhaps an implication that marriage is a bit like a mini republic or republics are basically a platonic polyamory of sorts...