In which I totally go after tangents instead of the main point:
If he’d just wanted Gwen to be happy, he should have just stepped aside. Or at least turned a blind eye.
Maybe this is just a reflection of what Arthurian fiction I've read-- and most of this was a long time ago, so I can't be super confident in my memory-- but I thought this was what happened. And that the tragedy of the situation was that, once their affair became known, the rules of society required him to be vengeful if he was going to maintain the loyalty of his other knights. I've always thought of it as a classic example of why the feudal system / obsession with blood-relatedness is terrible.
Imagine the glorious world we’d be living in if [Arthur/Gwen/Lance] was one of our mythic cornerstones, folks. Imagine a world where slash fiction didn’t exist because we were, all of us, constantly living the dream.
This is exactly what N. K. Jemisin's inheritance trilogy does, actually, and part of why it's so amazing. The trio of primal gods are not exactly in a functional state at the beginning in The Hundred Thousand Kingdoms (the first book), but it is pointedly not a traditional jealousy story, with the degree to which it is not revealed rather gradually.
(I'm slightly too lazy to figure out which of my email addresses I used to register a Wordpress account, or I'd leave this as a comment on the blog post itself. And it might be presumptuous telling a famous author to read someone else's book.)