Well... the Arthurian mythos doesn't really end well in most scenarios. Sword in the Stone just... kinda ends even if it's technically happy, Arthur's plot thread was never finished in Gargoyles even though it too went out on a high note, the most notable novel series where he comes back (as a ten year old) that I can think of was fucking terrible and every actual telling of his story ends with death, his kingdom falls, and Excalibur is taking a nap underwater until Storm Shadow snatches it up in the 80s.
And don't get me started on Fate/Stay....
Arthur getting a lady friend who legit loves him unconditionally and goes on awesome adventures and face hardships with him has appeal not because Hazel fan art is cute (though I imagine that has something to do with it...) but it gives a character who is typically characterized as a genuinely good or virtuous person a more deserving fate.
The only other truly awesome alternative I've ever seen is a defunct webcomic called The Path. Cthulhu and his minions are fucking shit up in the modern world, cultist cabals are kidnapping innocents, the mythical denizens of the world know everything's fucked.... and then King Arthur comes back. Fucking hell, forget the squirrel waifu, somebody bring THAT back.