Actually Guinever and Lancelot never did gave into their own temptation. It is true that they do lobe each other but their love was Arthur was much stronger so at nost, they only have secret meeting. But Morgan had expose their secret and lied about them sleeping together, thus resulting in Arthur believing her when he saw the both Lancelot and Guinevere together when they met up secretly.
In my book's version, at first, they did meet up secretly. That's when they truly respected and loved Arthur. But later on, after years passed, they did more. Yes, Morgan exposed their trahison to Arthur, so that Arthur (or his soldiers) really did find his wife and his best knight in a bed (naked). That's when they were arrested and called "criminals" or "outlaws". (Well, Guinever was arrested and almost hung, when Lancelot was able to run away and save her because he was the best knight of Camelot). After a lot of adventures, Arthur was able to forgive his wife and take her back at in the throne, but Lancelot never worked for Arthur again. That's when they weren't able to see each other again, but they never stopped being in love.
SPOILER ALERT!'!!
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Guys, in the real legend (I've read it before) Morgan is Arthur's ennemy and a witch (even if she is really her sister). She's also the woman Merlin loves (and the cause of his sadness/absence), and she once also used Lancelot to try to destroy Guenevievre (not sure about the grammar of her name though) because she was her brother's wife. As for Guenevievre, not only is she the Queen of Camelot, but she's Lancelot's lover. The two of them both betrayed Arthur because of their incredible strong love for each other. (They didn't do anything wrong against Arthur, they even highly respected him. But they were discovered in the same bed by Arthur's soldiers. And so, Arthur did get mad and he wanted to kill them) - they weren't kill by him.
And that was a little summary. The real book has about 500 pages, and it explains way more. It's really interesting though.
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So here's what I think about the last chapter of the manga.
--> It's just my opinion!
Because of my prediction about Morgan being the bad guy in the story is right, I'm pretty sure this is going to follow the legend.
So, when, at the end of the last chapter, Morgan says that she is the one who told Lancelot to save Ling ling, it's because she probably manipulated him. So Lancelot will, kind of, be a traitor to Arthur. BUT!! Because Lancelot is supposed to love Guenevievre, and Morgan already told Ling Ling that she used her (Guenevievre) as well before, and that she wasn't useful after all, i thinks that Guenevievre may be of help for Arthur now. She will want to get revenge on Morgan for using her, and Lancelot will help her too because he will love her (even if, in the manga, I personally despite her - Lancelot could have better). So in the end, Lancelot will be with Guenevievre, and Ling ling will somehow be able to go to Arthur! As for Merlin, he will also somehow come back and make everybody remember what has truly happened. Happy ending! ヾ(☆▽☆)