Sorry, Joe F, but I can't agree.

It was not part of the Laws of Chivalry that a married woman who is "love-struck" should attempt to sleep with the object of her affections. (Women, by the way, were not goverened by rules of chivalry anyway.) It was even less part of any chivalric code for a man to sleep with an inappropriate woman. Chivalric or courtly love was ideally non-sexual, with the man worshipping the woman and performing great feats in her honor. Entire romances, such as Sir Gawain and the Green Knight, are centered on the idea that the height of chivalry is refusing sexual contact with women if that contact is not socially appropriate (eg. you are not married to her, or worse, she is your lord's wife). In fact, Matty's inability to refuse her advances would be seen as emotional and womanly, "abandoning his manhood" in your words.

The page was also not bound by chivalric rules, and it is open to interpretation whether he did the right thing. He is, after all, a lady's page, that is, her servant, and he obviously goes against her wishes. On the other hand, in the medieval/renaissance worldview, Barnard is her boss, and hence the page's "boss's boss." So the situation is similar to being in an office where your boss does something which you know HER boss would not approve of. Do you tell? Hard to say, but few would argue that it's necessarily your JOB to tell.

Insofar as Barnard/Arlen goes, once he is informed by the page, he has more options than simply killing them on the spot. Depending on where his demesne is, he may be essentially an absolute tyrant on his own lands. Or he may be able to prosecute them legally. he certainly does not have to kill them, as he himself recognizes in some versions of the ballad where he regrets his actions afterward.

The good thing about the ballad for me is that it presents complexities of morality rarely seen in ballads. You can ask: was Lady Barnard wrong to pursue Matty, if she was in a loveless marriage? Was Matty wrong to accept her offer, if he could see how unhappy she was? Was the page wrong to tell, given what the likely consequences would be? Was Barnard wrong to kill them? In all cases, the answer is "yes...and no." That's why it's one of the great ones!