Le Morte D'Arthur
How we cite our quotes:
"But I fele by thy wordis that thou haste agreed to the deth of my persone: and therefore thou art a traytoure – but I wyte the lesse, for my sistir Morgan le Fay by hir false crauftis made the to agré to hir fals lustis." (90.30-33)
One of Arthur's own knights, Accalon, betrays him, hoping to become king by marrying the current king's sister, Morgan le Fay, and killing Arthur. Yet Arthur… forgives him? Later, Arthur's kingdom will be brought down by a similar betrayal by his own son. Maybe if Arthur should've made an example of Accalon instead of being so soft on him.
So uppon a day Sir Trystrames talked with La Beale Isode in a wyndowe, and that aspyed Sir Andred and tolde the kyng. Than Kyng Marke toke a swerde in his honde and cam to Sir Trystrames and called hym "false traytowre," and wolde have stryken hym. (266.19-22)
There's actually a double-dose of betrayal going on here. The one that probably first comes to mind is the affair between Trystram and Isode, which is a betrayal of King Mark. And the other? Andred's exposure of Trystram, his own cousin.
Than the kynge made his quene to drynke [from the horn], and an hondred ladyes with her; and there were but foure ladyes of all tho that dranke clene. "Alas!" seyde Kynge Marke, "this is a grete dyspyte," and swore a grete othe that she sholde be brente, and the other ladyes also. (269.4-8)
The magic horn from which only a faithful wife can "drink clean" reveals Isode to be unfaithful to Mark, which shocks a grand total of no one. Yet it also shows that Isode's in good company – apparently, adultery is widespread in Mark's court.